Assignment 6 Solution. Please do not copy and paste my answer. You will get similar questions but with different numbers!

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1 Assignment 6 Solution Please do not copy and paste my answer. You will get similar questions but with different numbers! This question tests you the following points: Integration by Parts: Let u = x, dv = cos(2x), then du = dx and v = dv = cos(2x)dx = 1 2 sin(2x). x cos(2x)dx = = x 1 2 sin(2x) 1 2 sin(2x)dx = 1 2 sin(2x)x + 1 cos(2x) +C 4 1

2 Integration by Parts: Let u = x 2 + 2x, dv = cos(x), then du = (2x + 2)dx = 2(x + 1) and v = dv = cos(x)dx = sin(x). x cos(2x)dx = = (x 2 + 2x)sin(x) 2 (x + 1)sin(x)dx Apply Integration by parts again to find (x + 1)sin(x)dx. Let u = x + 1 and dv = sin xdx, then du = dx and v = dv = sin xdx = cos x (x + 1)sin(x)dx = = (x + 1)cos x + = (x + 1)cos x + sin x cos xdx Plug back to the first step x cos(2x)dx = (x 2 + 2x)sin(x) 2 (x + 1)sin(x)dx = (x 2 + 2x)sin(x) 2( (x + 1)cos x + sin x) +C 2

3 Integration by Parts: Let u = tan 1 (8t), dv = dt, then du = 8 1+(8t) 2 dt = t 2 dt and v = dv = dt = t. tan 1 (8t)dt = = tan 1 (8t)t 8 t t 2 dt To find t dt, use u-substitution. Let u = t 2, then du = 128tdt or tdt = t du Plug back to the previous step: t t 2 dt = u du = ln u = ln t 2 = ln(1 + 64t 2 ) tan 1 (8t)dt = tan 1 t (8t)t t 2 dt = tan 1 (8t)t ln(1 + 64t 2 ) +C = tan 1 (8t)t 1 16 ln(1 + 64t 2 ) +C 3

4 Integration by Parts: Let u = ln p, dv = p 3 dp, then du = 1 p dp and v = dv = p 3 dp = 1 4 p4. p 3 ln pdp = p4 p dp = ln p 1 4 p4 = p4 ln p 4 = p4 ln p p 3 dp 1 16 p4 +C 4

5 Integration by Parts: Let u = sin(9θ), dv = e 8θ dθ, then du = 9cos(9θ)dθ and v = dv = e 8θ dθ = 1 8 e8θ. sin(9θ)e 8θ dθ = 1 8 e8θ 9cos(9θ)dθ e 8θ cos(9θ)dθ = sin(9θ) 1 8 e8θ = 1 8 sin(9θ)e8θ 9 8 To find e 8θ cos(9θ)dθ, apply integration by parts again. Let u = cos(9θ) and dv = e 8θ dθ, then du = 9sin(9θ)dθ and v = dv = e 8θ dθ = 1 8 e8θ. inte 8θ cos(9θ)dθ = 1 8 e8θ 9sin(9θ)dθ e 8θ sin(9θ)dθ = cos(9θ) 1 8 e8θ + = 1 8 cos(9θ)e8θ Now plug back to previous step: sin(9θ)e 8θ dθ = 1 8 sin(9θ)e8θ 9 8 e 8θ cos(9θ)dθ = 1 8 sin(9θ)e8θ 9 8 [ 1 8 cos(9θ)e8θ = 1 8 sin(9θ)e8θ 9 64 cos(9θ)e8θ e 8θ sin(9θ)dθ] e 8θ sin(9θ)dθ Then sin(9θ)e 8θ dθ e 8θ sin(9θ)dθ = 1 8 sin(9θ)e8θ 9 64 cos(9θ)e8θ e 8θ sin(9θ)dθ = 1 8 sin(9θ)e8θ 9 64 cos(9θ)e8θ e 8θ sin(9θ)dθ = [ 1 8 sin(9θ)e8θ 9 64 cos(9θ)e8θ ] +C 5

6 Integration by Parts: Let u = z 3, dv = e z dz, then du = 3z 2 dz and v = dv = e z dz = e z. z 3 e z = e z z 2 dz (a) = z 3 e z 3 To find e z z 2 dz, let u = z 2 and dv = e z dz, then du = 2z and v = e z. z 2 e z = e z zdz = z 2 e z 2 (b) To find e z zdz, let u = z and dv = e z dz, then du = z and v = e z. ze z = = ze z e z dz = ze z e z (c) Plug (c) into (b): z 2 e z = z 2 e z 2 e z zdz (b) = z 2 e z 2(ze z e z ) = z 2 e z 2ze z 2e z Then plug it back to (a) z 3 e z = z 3 e z 3 e z z 2 dz (a) = z 3 e z 3(z 2 e z 2ze z 2e z ) = z 3 e z 3z 2 e z + 6ze z 6e z So 19 z 3 e z = 19(z 3 e z 3z 2 e z + 6ze z 6e z ) 6

7 Integration by Parts: Let u = lnr, dv = r 3 dr, then du = 1 r dr and v = dv = 1 4 r 4. r 3 lnr = 1 4 r 4 1 r dr r 3 dr = 1 4 r 4 lnr = 1 4 r 4 lnr 1 4 = 1 4 r 4 lnr 1 16 r 4 +C Then 3 1 r 3 lnr = [ ln ] [ ln ] = 81 4 ln r 3 lnr = 9[ ln3 5] = 4 ln3 45 7

8 Integration by Parts: Let u = cos 1 x, dv = dx, then du = 1 1 x 2 dx and v = dv = x. cos 1 xdx = x = cos 1 (x)x + = cos 1 (x)x + 1 dx 1 x 2 x 1 x 2 dx To find x 1 x 2 dx, use u-substitution. Let u = 1 x2,then du = 2xdx or xdx = 1 2 du x dx = 1 1 x du = 1 u 2 2 u = 1 x 2 Plug back to the first part 7 cos 1 xdx = 7[ 1 π ] = 7π cos 1 xdx = cos 1 (x)x 1 x 2 = 1 π

9 Integration by Parts: Let u = r 2, dv = r 16+r 2 dr, then du = 2rdr and v = dv = 16 + r 2. r r 2 dr = = r r r 2 2rdr We can use u-substitution to find 16 + r 2 2rdr Let u = 16 + r 2, then du = 2rdr, 16 + r 2 2rdr = udu = 2 3 u 3 2 = 2 3 (16 + r 2 ) 3 2. Plug back to the previous step: r r 2 dr = r r r 2 2rdr = r r (16 + r 2 ) r r 2 dr = ( ) 3 2 [ ( ) 3 2 ] = (17) (16) 3 2 =

10 Integration by Parts: We do u-substitution first. Here I am going to use y instead of u. Let y = x, then d y = 1 2 x dx or dx = 2 xd y = 2yd y 7 cos xdx = 7 (cos y)2yd y = 14 y cos yd y Now use integration by parts: Let u = y, dv = cos(x), then du = d y and v = dv = cos(y)d y = sin(y). 7 cos xdx = 7 (cos y)2yd y = 14 y cos yd y = 14 udv = 14[uv ] = 14[y sin(y) sin(y)d y] = 14[y sin y + cos y] = 14[ x sin x + cos x] +C 10

11 Integration by Parts: We do u-substitution first. Here I am going to use y instead of u. Let y = x + 3, then d y = dx and x = y 3 x ln(3 + x)dx = (y 3)ln yd y Now use integration by parts: Let u = ln y, dv = (y 3), then du = 1 y d y and v = dv = (y 3)d y = 1 2 y 2 3y. x ln(3 + x)dx = (y 3)ln yd y = udv = [uv ] = ( 1 2 y 2 3y)ln y ( 1 2 y 2 3y) 1 y d y = ( 1 2 y 2 3y)ln y ( 1 2 y 3)d y = ( 1 2 y 2 3y)ln y 1 4 y 2 + 3y +C = [ 1 2 (x + 3)2 3(x + 3)]ln(x + 3) 1 4 (x + 3)2 + 3(x + 3) +C 11

12 Integration by Parts: let u = x, dv = f (x)dx, then du = dx and v = f (x)dx = f (x). x f (x)dx = udv = uv = x f (x) f (x)dx = x f (x) f (x) 4 1 x f (x)dx = 4f (4) f (4) [1f (1) f (1)] = [1 3 1] = 1 12