Step 1: Separate the integral into two parts.
∫x3+6x2+x−15−5xdx=∫x3dx+∫6x2+x−15−5xdx
Step 2: Integrate the first term.
∫x3dx=3+1x3+1+C1=4x4+C1
Step 3: Factor the denominator of the second term.
The denominator is 6x2+x−1. We look for two numbers that multiply to 6×(−1)=−6 and add to 1. These numbers are 3 and −2.
6x2+x−1=6x2+3x−2x−1=3x(2x+1)−1(2x+1)=(3x−1)(2x+1)
Step 4: Set up the partial fraction decomposition for the rational function.
(3x−1)(2x+1)5−5x=3x−1A+2x+1B
Multiply both sides by (3x−1)(2x+1):
5−5x=A(2x+1)+B(3x−1)
Step 5: Solve for the constants A and B.
To find A, set 3x−1=0⟹x=31:
5−5(31)=A(2(31)+1)+B(0)
5−35=A(32+1)
315−5=A(35)
310=35A⟹A=2
To find B, set 2x+1=0⟹x=−21:
5−5(−21)=A(0)+B(3(−21)−1)
5+25=B(−23−1)
210+5=B(−25)
215=−25B⟹B=−3
So, the partial fraction decomposition is:
6x2+x−15−5x=3x−12−2x+13
Step 6: Integrate the partial fractions.
∫(3x−12−2x+13)dx=∫3x−12dx−∫2x+13dx
For ∫3x−12dx: Let u=3x−1, du=3dx.
∫u231du=32∫u1du=32ln∣u∣=32ln∣3x−1∣
For ∫2x+13dx: Let v=2x+1, dv=2dx.
∫v321dv=23∫v1dv=23ln∣v∣=23ln∣2x+1∣
Combining these, we get:
∫6x2+x−15−5xdx=32ln∣3x−1∣−23ln∣2x+1∣+C2
Step 7: Combine the results from Step 2 and Step 6.
∫x3+6x2+x−15−5xdx=4x4+32ln∣3x−1∣−23ln∣2x+1∣+C
The final answer is 4x4+32ln∣3x−1∣−23ln∣2x+1∣+C.