Here are the solutions to Question 2:
Question 2 (a)
a) To evaluate ∫xlnxdx, we use integration by parts, ∫udv=uv−∫vdu.
Step 1: Choose u=lnx and dv=xdx.
Step 2: Differentiate u and integrate dv:
du=x1dx
v=∫xdx=2x2
Step 3: Apply the integration by parts formula:
∫xlnxdx=(lnx)(2x2)−∫(2x2)(x1)dx
Step 4: Simplify and integrate the remaining term:
=2x2lnx−∫2xdx
=2x2lnx−21(2x2)+C
2x2lnx−4x2+C
b) To evaluate ∫xsinxdx, we use integration by parts.
Step 1: Choose u=x and dv=sinxdx.
Step 2: Differentiate u and integrate dv:
du=dx
v=∫sinxdx=−cosx
Step 3: Apply the integration by parts formula:
∫xsinxdx=(x)(−cosx)−∫(−cosx)dx
Step 4: Simplify and integrate the remaining term:
=−xcosx+∫cosxdx
−xcosx+sinx+C
c) To evaluate ∫x2e3xdx, we use integration by parts twice.
Step 1: For the first application, choose u=x2 and dv=e3xdx.
Step 2: Differentiate u and integrate dv:
du=2xdx
v=∫e3xdx=31e3x
Step 3: Apply the integration by parts formula:
∫x2e3xdx=x2(31e3x)−∫(31e3x)(2x)dx
=31x2e3x−32∫xe3xdx
Step 4: Now, evaluate ∫xe3xdx using integration by parts again. Choose u=x and dv=e3xdx.
Step 5: Differentiate u and integrate dv:
du=dx
v=∫e3xdx=31e3x
Step 6: Apply the integration by parts formula for the second time:
∫xe3xdx=x(31e3x)−∫(31e3x)dx
=31xe3x−31(31e3x)+C1
=31xe3x−91e3x+C1
Step 7: Substitute this result back into the expression from Step 3:
∫x2e3xdx=31x2e3x−32(31xe3x−91e3x)+C
31x2e3x−92xe3x+272e3x+C
Question 2 (b)
a) To evaluate ∫x2−3x+2x+1dx, we use partial fraction decomposition.
Step 1: Factor the denominator: x2−3x+2=(x−1)(x−2).
Step 2: Set up the partial fraction decomposition:
(x−1)(x−2)x+1=x−1A+x−2B
Multiply both sides by (x−1)(x−2):
x+1=A(x−2)+B(x−1)
Step 3: Solve for A and B.
Set x=1: 1+1=A(1−2)⟹2=−A⟹A=−2.
Set x=2: 2+1=B(2−1)⟹3=B⟹B=3.
Step 4: Rewrite the integral using the partial fractions and integrate:
∫(x−1−2+x−23)dx=−2∫x−11dx+3∫x−21dx
−2ln∣x−1∣+3ln∣x−2∣+C
b) To evaluate ∫(x+2)2x2+1dx, we can manipulate the numerator.
Step 1: Let y=x+2, so x=y−2. Substitute this into the numerator:
x2+1=(y−2)2+1=(y2−4y+4)+1=y2−4y+5
Step 2: Substitute y back into the integral. Note that dx=dy:
∫y2y2−4y+5dy
Step 3: Split the fraction into simpler terms:
=∫(y2y2−y24y+y25)dy=∫(1−y4+5y−2)dy
Step 4: Integrate each term with respect to y:
=y−4ln∣y∣+5(−1y−1)+C
=y−4ln∣y∣−y5+C
Step 5: Substitute back y=x+2:
x+2−4ln∣x+2∣−x+25+C
That's 2 down. 3 left today — send the next one.