here is the solution to question 4:
a)
i) ∫3x(2−x2)21dx;
Step 1: Use substitution.
Let u=2−x2.
Then, differentiate u with respect to x: dxdu=−2x.
Rearrange to find dx: dx=−2xdu.
Substitute u and dx into the integral:
∫3x(u)21(−2xdu)
Step 2: Simplify and integrate with respect to u.
The x terms cancel out:
∫−23u21du
Integrate using the power rule ∫undu=n+1un+1+C:
−23⋅21+1u21+1+C
−23⋅23u23+C
−u23+C
Step 3: Substitute back u=2−x2.
−(2−x2)+32C
ii) ∫x2cos3xdx;
Step 1: Use integration by parts, ∫udv=uv−∫vdu.
Let u=x2 and dv=cos3xdx.
Then du=2xdx and v=∫cos3xdx=31sin3x.
∫x2cos3xdx=x2(31sin3x)−∫(31sin3x)(2xdx)
=31x2sin3x−32∫xsin3xdx
Step 2: Apply integration by parts again for ∫xsin3xdx.
Let u1=x and dv1=sin3xdx.
Then du1=dx and v1=∫sin3xdx=−31cos3x.
∫xsin3xdx=x(−31cos3x)−∫(−31cos3x)dx
=−31xcos3x+31∫cos3xdx
=−31xcos3x+31(31sin3x)+C1
=−31xcos3x+91sin3x+C1
Step 3: Substitute the result back into the main integral.
31x2sin3x−32(−31xcos3x+91sin3x)+C
=31x2sin3x+92xcos3x−272sin3x+C
The integral is 31x2sin3x+92xcos3x−272sin3x+C.
iii) ∫x2+2x−322−6xdx;
Step 1: Factor the denominator and perform partial fraction decomposition.
The denominator is x2+2x−3=(x+3)(x−1).
Set up the partial fractions:
(x+3)(x−1)22−6x=x+3A+x−1B
Multiply both sides by (x+3)(x−1):
22−6x=A(x−1)+B(x+3)
To find A, set x=−3:
22−6(−3)=A(−3−1)+B(−3+3)
22+18=−4A
40=−4A⟹A=−10
To find B, set x=1:
22−6(1)=A(1−1)+B(1+3)
16=4B⟹B=4
Step 2: Rewrite the integral using partial fractions.
∫(x+3−10+x−14)dx
Step 3: Integrate each term.
−10∫x+31dx+4∫x−11dx
=−10ln∣x+3∣+4ln∣x−1∣+C
The integral is −10ln∣x+3∣+4ln∣x−1∣+C.
b)
To determine the area of the region bounded by the parabola y=x2+4 and the straight line y=x+6.
Step 1: Find the points of intersection of the two curves.
Set the equations equal to each other:
x2+4=x+6
Rearrange into a quadratic equation:
x2−x−2=0
Factor the quadratic equation:
(x−2)(x+1)=0
The points of intersection are x=−1 and x=2. These will be the limits of integration.
Step 2: Determine which function is above the other in the interval [−1,2].
Choose a test point within the interval, for example, x=0.
For the parabola: y=(0)2+4=4.
For the line: y=0+6=6.
Since 6>4, the line y=x+6 is above the parabola y=x2+4 in the interval [−1,2].
Step 3: Set up the definite integral for the area.
The area A is given by the integral of the upper function minus the lower function:
A=∫−12((x+6)−(x2+4))dx
A=∫−12(−x2+x+2)dx
Step 4: Evaluate the definite integral.
Integrate term by term:
A=[−3x3+2x2+2x]−12
Apply the limits of integration:
A=(−3(2)3+2(2)2+2(2))−(−3(−1)3+2(−1)2+2(−1))
A=(−38+24+4)−(−3−1+21−2)
A=(−38+2+4)−(31+21−2)
A=(−38+6)−(31+21−24)
A=(3−8+18)−(62+3−12)
A=310−(−67)
A=310+67
Find a common denominator:
A=620+67
A=627
Simplify the fraction:
A=29
The area of the region is 29squareunits.
You're doing great! What's next?