FAD1014 — 1-Hour Mechanical Speed Drill
Fast. Repetitive. Builds instant recall. No deep theory — just write the answer and move.
Targets: Part A basics (standard integrals, substitution, binomial, conic ID) + Maclaurin Series (leaked).
Rules: 5 min per mini-section. If stuck >30s, skip and check solution. Do each section twice if time.
BLOCK 1: STANDARD INTEGRALS — MUST BE INSTANT (5 min)
Q1
$$\int x^5,dx$$
Q2
$$\int \frac{1}{x},dx$$
Q3
$$\int e^{3x},dx$$
Q4
$$\int \sin 2x,dx$$
Q5
$$\int \cos 4x,dx$$
Q6
$$\int \sec^2 x,dx$$
Q7
$$\int \frac{1}{\sqrt{1-x^2}},dx$$
Q8
$$\int \frac{1}{1+x^2},dx$$
Q9
$$\int \frac{1}{\sqrt{4-x^2}},dx$$
Q10
$$\int (2x+3)^5,dx$$
BLOCK 2: U-SUBSTITUTION (5 min)
Q11
$$\int x,e^{x^2},dx$$
Q12
$$\int \frac{x}{x^2+1},dx$$
Q13
$$\int x^2 \cos(x^3),dx$$
Q14
$$\int \frac{2x}{\sqrt{x^2+4}},dx$$
Q15
$$\int x\sqrt{x^2+1},dx$$
BLOCK 3: DEFINITE INTEGRALS (5 min)
Q16
$$\int_0^{\pi/2} \sin x,dx$$
Q17
$$\int_0^1 e^{2x},dx$$
Q18
$$\int_1^e \frac{1}{x},dx$$
Q19
$$\int_0^{\pi/4} \sec^2 x,dx$$
Q20
$$\int_0^2 (3x^2 + 2x),dx$$
BLOCK 4: AREA UNDER CURVE (5 min)
Q21
Area under $y = x^2$ from $x=0$ to $x=2$.
Q22
Area under $y = e^x$ from $x=0$ to $x=\ln 3$.
Q23
Area under $y = \sin x$ from $x=0$ to $x=\pi$.
Q24
Area under $y = \frac{1}{x}$ from $x=1$ to $x=e$.
BLOCK 5: BINOMIAL I (5 min)
Q25
State $\binom{7}{2}$, $\binom{8}{3}$, $\binom{10}{4}$.
Q26
Expand $(2x+1)^4$ completely.
Q27
Expand $(x-2)^5$ completely.
Q28
Find coefficient of $x^3$ in $(1+2x)^6$.
Q29
Find coefficient of $x^2$ in $(x-3)^5$.
Q30
Find coefficient of $x^4$ in $(x^2-2)^6$.
BLOCK 6: SERIES CONVERGENCE / METHOD OF DIFFERENCES (5 min)
Q31
Does $a_n = \frac{2n^2+3}{5n^2-2n+1}$ converge? Find the limit if so.
Q32
Does $\sum_{n=1}^\infty \frac{n}{2n+1}$ converge or diverge?
Q33
Evaluate $\sum_{r=1}^{20} (3r-1)$.
Q34
Evaluate $\sum_{r=1}^{n} \frac{1}{r(r+1)}$.
Q35
Evaluate $\sum_{r=1}^{n} \frac{2}{r(r+2)}$.
BLOCK 7: CONIC ID — QUICK FIRE (5 min)
Q36
$(x-2)^2 = 8(y+3)$. State vertex, focus, directrix, direction.
Q37
$y^2 = -12(x-1)$. State vertex, focus, directrix, direction.
Q38
$\frac{x^2}{25} + \frac{y^2}{9} = 1$. State centre, vertices, foci. Horizontal or vertical?
Q39
$\frac{(x+1)^2}{4} + \frac{(y-2)^2}{16} = 1$. State centre, vertices, foci.
Q40
$\frac{x^2}{16} - \frac{y^2}{9} = 1$. State centre, vertices, foci, asymptotes.
Q41
$\frac{(y-1)^2}{4} - \frac{(x+2)^2}{9} = 1$. State centre, vertices, asymptotes.
BLOCK 8: MACLAURIN — STANDARD FORMS (5 min)
Q42
$$e^x = ?$$
Q43
$$\sin x = ?$$
Q44
$$\cos x = ?$$
Q45
$$\ln(1+x) = ?$$
Q46
$$\frac{1}{1-x} = ?$$
Q47
$$\sinh x = ?$$
Q48
$$\cosh x = ?$$
Q49
$$\arctan x = ?$$
BLOCK 9: MACLAURIN — SUBSTITUTION (8 min)
Q50
$$e^{-2x}$$
Q51
$$e^{x^2}$$
Q52
$$\sin(3x^2)$$
Q53
$$\cos(2x^3)$$
Q54
$$\ln(1+4x)$$
Q55
$$x e^{-x}$$
Q56
$$x^2 \cos x$$
Q57
$$\frac{1}{1+3x}$$
BLOCK 10: MACLAURIN — MULTIPLICATION & INTEGRATION (7 min)
Q58
Find up to $x^3$: $e^x \sin x$
Q59
Find up to $x^4$: $e^{-x} \cos x$
Q60
Use series to approximate: $\displaystyle\int_0^{0.5} e^{-x^2},dx$ (3 d.p.)
Q61
Find series for $\displaystyle\int \frac{\sin x}{x},dx$ up to $x^5$ term.
Q62
Derive $\tan x$ up to $x^3$ using $f(0), f'(0), f''(0), f'''(0)$.
SOLUTIONS
BLOCK 1
Q1
$$\frac{x^6}{6} + C$$
Q2
$$\ln|x| + C$$
Q3
$$\frac13 e^{3x} + C$$
Q4
$$-\frac12 \cos 2x + C$$
Q5
$$\frac14 \sin 4x + C$$
Q6
$$\tan x + C$$
Q7
$$\sin^{-1} x + C$$
Q8
$$\tan^{-1} x + C$$
Q9
$$\sin^{-1}\left(\frac{x}{2}\right) + C$$
Q10
$\frac{1}{12}(2x+3)^6 + C$ (let $u=2x+3$, $du=2dx$)
BLOCK 2
Q11
$u=x^2$, $du=2x,dx$ → $\frac12\int e^u,du = \frac12 e^{x^2} + C$
Q12
$u=x^2+1$, $du=2x,dx$ → $\frac12\int\frac{du}{u} = \frac12\ln(x^2+1) + C$
Q13
$u=x^3$, $du=3x^2,dx$ → $\frac13\int\cos u,du = \frac13\sin(x^3) + C$
Q14
$u=x^2+4$, $du=2x,dx$ → $\int u^{-1/2},du = 2\sqrt{x^2+4} + C$
Q15
$u=x^2+1$, $du=2x,dx$ → $\frac12\int u^{1/2},du = \frac13(x^2+1)^{3/2} + C$
BLOCK 3
Q16
$$[-\cos x]_0^{\pi/2} = 0 - (-1) = 1$$
Q17
$$\left[\frac12 e^{2x}\right]_0^1 = \frac12 e^2 - \frac12 = \frac12(e^2-1)$$
Q18
$$[\ln x]_1^e = 1 - 0 = 1$$
Q19
$$[\tan x]_0^{\pi/4} = 1 - 0 = 1$$
Q20
$$[x^3 + x^2]_0^2 = (8+4) - 0 = 12$$
BLOCK 4
Q21
$$\int_0^2 x^2,dx = \left[\frac{x^3}{3}\right]_0^2 = \frac83$$
Q22
$$\int_0^{\ln 3} e^x,dx = [e^x]_0^{\ln 3} = 3 - 1 = 2$$
Q23
$$\int_0^\pi \sin x,dx = [-\cos x]_0^\pi = 1 - (-1) = 2$$
Q24
$$\int_1^e \frac1x,dx = [\ln x]_1^e = 1 - 0 = 1$$
BLOCK 5
Q25
$\binom{7}{2}=21$, $\binom{8}{3}=56$, $\binom{10}{4}=210$
Q26
$$(2x)^4 + 4(2x)^3(1) + 6(2x)^2(1)^2 + 4(2x)(1)^3 + 1^4$$ $$= 16x^4 + 32x^3 + 24x^2 + 8x + 1$$
Q27
$$x^5 + 5x^4(-2) + 10x^3(-2)^2 + 10x^2(-2)^3 + 5x(-2)^4 + (-2)^5$$ $$= x^5 - 10x^4 + 40x^3 - 80x^2 + 80x - 32$$
Q28
$$\binom{6}{3}(1)^3(2x)^3 = 20 \cdot 8x^3 = 160$$
Q29
$\binom{5}{2}x^2(-3)^3$... Wait: $(x-3)^5$, term with $x^2$: need $r=3$ (since $b=-3$, $a=x$, $n=5$, term $r$ has $a^{5-r}b^r$) $$\binom{5}{3}x^2(-3)^3 = 10 \cdot (-27)x^2 = -270$$
Q30
$(x^2-2)^6$, need $(x^2)^2 = x^4$ → $r=4$? No: $a=x^2$, $b=-2$, need $a^{6-r} = (x^2)^{6-r} = x^{12-2r} = x^4$ → $12-2r=4$ → $r=4$ $$\binom{6}{4}(x^2)^2(-2)^4 = 15 \cdot 16 = 240$$
BLOCK 6
Q31
$\lim_{n\to\infty} \frac{2n^2+3}{5n^2-2n+1} = \frac{2}{5}$ → Converges
Q32
$\lim_{n\to\infty} \frac{n}{2n+1} = \frac12 \neq 0$ → Diverges (nth term test)
Q33
$$3\sum r - \sum 1 = 3\cdot\frac{20\cdot21}{2} - 20 = 630 - 20 = 610$$
Q34
$\frac{1}{r(r+1)} = \frac1r - \frac1{r+1}$ → $1 - \frac1{n+1} = \frac{n}{n+1}$
Q35
$$\frac{2}{r(r+2)} = \frac1r - \frac1{r+2}$$ Telescopes: $1 + \frac12 - \frac1{n+1} - \frac1{n+2} = \frac32 - \frac1{n+1} - \frac1{n+2}$
BLOCK 7
Q36
Vertex $(2,-3)$. $4a=8$ → $a=2$. Opens up. Focus $(2,-1)$. Directrix $y=-5$.
Q37
Vertex $(1,0)$. $4a=12$ → $a=3$. Opens left. Focus $(-2,0)$. Directrix $x=4$.
Q38
Centre $(0,0)$. $a=5$, $b=3$ (horizontal). $c=\sqrt{25-9}=4$. Vertices $(\pm5,0)$. Foci $(\pm4,0)$.
Q39
Centre $(-1,2)$. $a=2$, $b=4$ (vertical). $c=\sqrt{16-4}=2\sqrt3$. Vertices $(-1,6)$ and $(-1,-2)$. Foci $(-1,2\pm2\sqrt3)$.
Q40
Centre $(0,0)$, horizontal. $a=4$, $b=3$. $c=\sqrt{16+9}=5$. Vertices $(\pm4,0)$. Foci $(\pm5,0)$. Asymptotes $y = \pm\frac34 x$.
Q41
Centre $(-2,1)$, vertical. $a=2$, $b=3$. $c=\sqrt{4+9}=\sqrt{13}$. Vertices $(-2,3)$ and $(-2,-1)$. Asymptotes $y-1 = \pm\frac23(x+2)$.
BLOCK 8
Q42
$$1 + x + \frac{x^2}{2!} + \frac{x^3}{3!} + \frac{x^4}{4!} + \cdots$$
Q43
$$x - \frac{x^3}{3!} + \frac{x^5}{5!} - \frac{x^7}{7!} + \cdots$$
Q44
$$1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \frac{x^6}{6!} + \cdots$$
Q45
$$x - \frac{x^2}{2} + \frac{x^3}{3} - \frac{x^4}{4} + \cdots \quad (-1 < x \leq 1)$$
Q46
$$1 + x + x^2 + x^3 + \cdots \quad (|x| < 1)$$
Q47
$$x + \frac{x^3}{3!} + \frac{x^5}{5!} + \cdots$$
Q48
$$1 + \frac{x^2}{2!} + \frac{x^4}{4!} + \cdots$$
Q49
$$x - \frac{x^3}{3} + \frac{x^5}{5} - \frac{x^7}{7} + \cdots$$
BLOCK 9
Q50
$e^{-2x} = 1 - 2x + \frac{4x^2}{2!} - \frac{8x^3}{3!} + \frac{16x^4}{4!} + \cdots$ $= 1 - 2x + 2x^2 - \frac{4x^3}{3} + \frac{2x^4}{3} + \cdots$
Q51
$$e^{x^2} = 1 + x^2 + \frac{x^4}{2!} + \frac{x^6}{3!} + \cdots$$
Q52
$\sin(3x^2) = 3x^2 - \frac{(3x^2)^3}{3!} + \cdots$ → up to $x^4$: just $3x^2$
Q53
$\cos(2x^3) = 1 - \frac{(2x^3)^2}{2!} + \cdots$ → up to $x^4$: just $1$
Q54
$\ln(1+4x) = 4x - \frac{16x^2}{2} + \frac{64x^3}{3} - \frac{256x^4}{4} + \cdots$ $= 4x - 8x^2 + \frac{64x^3}{3} - 64x^4 + \cdots$
Q55
$x e^{-x} = x\left(1 - x + \frac{x^2}{2!} - \frac{x^3}{3!} + \cdots\right)$ $= x - x^2 + \frac{x^3}{2} - \frac{x^4}{6} + \cdots$
Q56
$x^2 \cos x = x^2\left(1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \cdots\right)$ $= x^2 - \frac{x^4}{2} + \cdots$ (up to $x^4$)
Q57
$\frac{1}{1+3x} = \frac{1}{1-(-3x)} = 1 + (-3x) + (-3x)^2 + (-3x)^3 + \cdots$ $= 1 - 3x + 9x^2 - 27x^3 + \cdots$
BLOCK 10
Q58
$$e^x\sin x = (1 + x + \frac{x^2}{2} + \frac{x^3}{6})(x - \frac{x^3}{6})$$
$x$: $x$ $x^2$: $x^2$ $x^3$: $-\frac{x^3}{6} + \frac{x^3}{2} = \frac{x^3}{3}$
$$\boxed{x + x^2 + \frac{x^3}{3} + \cdots}$$
Q59
$$e^{-x}\cos x = (1 - x + \frac{x^2}{2} - \frac{x^3}{6} + \frac{x^4}{24})(1 - \frac{x^2}{2} + \frac{x^4}{24})$$
Up to $x^4$: $1$: $1$ $x$: $-x$ $x^2$: $-\frac12 + \frac12 = 0$ $x^3$: $\frac{x^3}{6} + \frac{x^3}{2} = -\frac16 + \frac12 = \frac13 x^3$... wait let me be careful.
$$1\cdot1 = 1$$ $$1(-\frac{x^2}{2}) + (-x)(1) = -\frac{x^2}{2} - x$$ $$1(\frac{x^4}{24}) + (-x)(-\frac{x^2}{2}) + (\frac{x^2}{2})(1) = \frac{x^4}{24} + \frac{x^3}{2} + \frac{x^2}{2}$$
Actually let me be systematic:
- Constant: $1\cdot1 = 1$
- $x$: $(-x)(1) = -x$
- $x^2$: $1(-\frac{x^2}{2}) + (\frac{x^2}{2})(1) = -\frac12 + \frac12 = 0$
- $x^3$: $(-x)(-\frac{x^2}{2}) + (-\frac{x^3}{6})(1) = \frac{x^3}{2} - \frac{x^3}{6} = \frac{x^3}{3}$
- $x^4$: $1(\frac{x^4}{24}) + (\frac{x^2}{2})(-\frac{x^2}{2}) + (\frac{x^4}{24})(1) = \frac1{24} - \frac14 + \frac1{24} = \frac1{24} - \frac6{24} + \frac1{24} = -\frac4{24} = -\frac16$
$$\boxed{1 - x + \frac{x^3}{3} - \frac{x^4}{6} + \cdots}$$
Q60
$$e^{-x^2} = 1 - x^2 + \frac{x^4}{2!} - \cdots$$
$$\int_0^{0.5} e^{-x^2},dx \approx \int_0^{0.5} \left(1 - x^2 + \frac{x^4}{2}\right)dx$$
$$= \left[x - \frac{x^3}{3} + \frac{x^5}{10}\right]_0^{0.5}$$
$$= 0.5 - \frac{0.125}{3} + \frac{0.03125}{10}$$
$= 0.5 - 0.041667 + 0.003125 = \boxed{0.461}$ (3 d.p.)
Q61
$$\frac{\sin x}{x} = \frac{x - \frac{x^3}{6} + \frac{x^5}{120} - \cdots}{x} = 1 - \frac{x^2}{6} + \frac{x^4}{120} - \cdots$$
$$\int \frac{\sin x}{x},dx = \int \left(1 - \frac{x^2}{6} + \frac{x^4}{120} - \cdots\right)dx$$
$$= x - \frac{x^3}{18} + \frac{x^5}{600} - \cdots + C$$
Q62
$$f(x) = \tan x$$
$$f(0) = 0$$ $f'(x) = \sec^2 x$, $f'(0) = 1$ $f''(x) = 2\sec^2 x \tan x$, $f''(0) = 0$ $f'''(x) = 4\sec^2 x \tan^2 x + 2\sec^4 x$, $f'''(0) = 2$
$$\tan x = x + \frac{x^3}{3} + \cdots$$
BLOCK 11: PART B WILDCARDS (15 min)
Integration by Parts (6 min)
Q63
$$\int x e^x,dx$$
Q64
$$\int x \ln x,dx$$
Q65
$$\int x^2 \ln x,dx$$
Q66
$$\int_0^1 x e^x,dx$$
Homogeneous DE (5 min)
Q67
$$\frac{dy}{dx} = \frac{x^2 + y^2}{xy}$$
Q68
$$\frac{dy}{dx} = \frac{x^2 + 2xy}{y^2}, \quad y(1) = 1$$
Trig Substitution or Parametric — Pick One (4 min)
Pick the one you're more comfortable with.
Q69a (Trig Sub)
$$\int \frac{dx}{\sqrt{4 - x^2}}$$
Q70a (Trig Sub)
$$\int \frac{dx}{\sqrt{x^2 + 9}}$$
OR
Q69b (Parametric)
$x = t^2$, $y = t^3$. Find $\frac{dy}{dx}$ and tangent at $t = 1$.
Q70b (Parametric)
$x = \cos t$, $y = \sin t$. Find $\frac{dy}{dx}$ and $\frac{d^2y}{dx^2}$.
SOLUTIONS — BLOCK 11
Integration by Parts
Q63
$u = x$, $dv = e^x,dx$ → $du = dx$, $v = e^x$ $$\int x e^x,dx = x e^x - \int e^x,dx = \boxed{x e^x - e^x + C}$$
Q64
$u = \ln x$, $dv = x,dx$ → $du = \frac1x,dx$, $v = \frac{x^2}{2}$ $$\int x\ln x,dx = \frac{x^2}{2}\ln x - \int \frac{x}{2},dx = \boxed{\frac{x^2}{2}\ln x - \frac{x^2}{4} + C}$$
Q65
$u = \ln x$, $dv = x^2,dx$ → $du = \frac1x,dx$, $v = \frac{x^3}{3}$ $$\int x^2\ln x,dx = \frac{x^3}{3}\ln x - \int \frac{x^2}{3},dx = \boxed{\frac{x^3}{3}\ln x - \frac{x^3}{9} + C}$$
Q66
$$\int_0^1 x e^x,dx = \left[x e^x - e^x\right]_0^1 = (e - e) - (0 - 1) = \boxed{1}$$
Homogeneous DE
Q67
$y = vx$, $\frac{dy}{dx} = v + x\frac{dv}{dx}$
$$v + x\frac{dv}{dx} = \frac{x^2 + v^2 x^2}{x \cdot vx} = \frac{1 + v^2}{v}$$
$$x\frac{dv}{dx} = \frac{1 + v^2}{v} - v = \frac{1}{v}$$
$v,dv = \frac{dx}{x}$ → $\frac{v^2}{2} = \ln|x| + C$
$$\boxed{y^2 = 2x^2(\ln|x| + C)}$$
Q68
$y = vx$, $v + x\frac{dv}{dx} = \frac{x^2 + 2vx^2}{v^2 x^2} = \frac{1 + 2v}{v^2}$
$$x\frac{dv}{dx} = \frac{1 + 2v}{v^2} - v = \frac{1 + 2v - v^3}{v^2}$$
This gets messy. Let's try: actually $\frac{x^2 + 2xy}{y^2} = \frac{x^2 + 2x(vx)}{(vx)^2} = \frac{x^2(1 + 2v)}{v^2 x^2} = \frac{1 + 2v}{v^2}$
$$x\frac{dv}{dx} = \frac{1 + 2v}{v^2} - v = \frac{1 + 2v - v^3}{v^2}$$
This is separable but the integration is hard. Let me use a simpler example instead.
Actually, replace Q68 with this:
Q68 (revised)
$$\frac{dy}{dx} = \frac{y}{x} + \frac{x}{y}, \quad y(1) = 1$$
$y = vx$, $v + xv' = v + \frac{1}{v}$
$xv' = \frac{1}{v}$ → $v,dv = \frac{dx}{x}$ → $\frac{v^2}{2} = \ln|x| + C$
$$\frac{y^2}{2x^2} = \ln|x| + C$$
$y(1) = 1$ → $\frac12 = C$
$$\boxed{y^2 = 2x^2\left(\ln|x| + \frac12\right)}$$
Trig Substitution
Q69a
$x = 2\sin\theta$, $dx = 2\cos\theta,dθ$ $$\int \frac{2\cos\theta,dθ}{2\cos\theta} = \int dθ = \theta + C = \boxed{\sin^{-1}\left(\frac{x}{2}\right) + C}$$
Q70a
$x = 3\tan\theta$, $dx = 3\sec^2\theta,dθ$ $$\int \frac{3\sec^2\theta,dθ}{3\sec\theta} = \int \sec\theta,dθ = \ln|\sec\theta + \tan\theta| + C$$ $$= \boxed{\ln\left|\frac{x}{3} + \frac{\sqrt{x^2+9}}{3}\right| + C = \ln\left|x + \sqrt{x^2+9}\right| + C'}$$
Parametric
Q69b
$$\frac{dy}{dx} = \frac{dy/dt}{dx/dt} = \frac{3t^2}{2t} = \frac{3t}{2}$$
At $t=1$: $x=1$, $y=1$, slope $= \frac32$
Tangent: $y - 1 = \frac32(x - 1)$ → $\boxed{3x - 2y = 1}$
Q70b
$$\frac{dy}{dx} = \frac{\cos t}{-\sin t} = \boxed{-\cot t}$$
$$\frac{d^2y}{dx^2} = \frac{d}{dt}(-\cot t) \big/ \frac{dx}{dt} = \frac{\csc^2 t}{-\sin t} = \boxed{-\csc^3 t}$$
APPENDIX: MUST-KNOW FORMULAS (CUT OUT + KEEP)
Part A Essentials
| Formula | Answer |
|---|---|
| $\int x^n,dx$ | $\frac{x^{n+1}}{n+1} + C$ |
| $\int \frac1x,dx$ | $\ln |
| $\int e^{ax},dx$ | $\frac1a e^{ax} + C$ |
| $\int \sin(ax),dx$ | $-\frac1a \cos(ax) + C$ |
| $\int \cos(ax),dx$ | $\frac1a \sin(ax) + C$ |
| $\int \sec^2 x,dx$ | $\tan x + C$ |
| $\int \frac{dx}{\sqrt{a^2-x^2}}$ | $\sin^{-1}(\frac{x}{a}) + C$ |
| $\int \frac{dx}{a^2+x^2}$ | $\frac1a\tan^{-1}(\frac{x}{a}) + C$ |
Binomial
$$(a+b)^n = \sum_{r=0}^n \binom{n}{r} a^{n-r}b^r$$
Maclaurin
$$f(x) = \sum_{n=0}^\infty \frac{f^{(n)}(0)}{n!}x^n$$
Conic Quick Reference
| Shape | $c^2$ formula |
|---|---|
| Ellipse | $c^2 = a^2 - b^2$ |
| Hyperbola | $c^2 = a^2 + b^2$ |
| Parabola form | Opens | Focus | Directrix |
|---|---|---|---|
| $(x-h)^2 = 4a(y-k)$ | Up | $(h,k+a)$ | $y=k-a$ |
| $(x-h)^2 = -4a(y-k)$ | Down | $(h,k-a)$ | $y=k+a$ |
| $(y-k)^2 = 4a(x-h)$ | Right | $(h+a,k)$ | $x=h-a$ |
| $(y-k)^2 = -4a(x-h)$ | Left | $(h-a,k)$ | $x=h+a$ |