let's integrate this rational function using partial fraction decomposition.
The integral is ∫(x2+4)(x−1)53+17x−7dx.
Step 1: Simplify the numerator.
53+17x−7=125+17x−7=17x+118
So the integral becomes:
∫(x2+4)(x−1)17x+118dx
Step 2: Set up the partial fraction decomposition.
Since (x2+4) is an irreducible quadratic factor and (x−1) is a linear factor, the decomposition takes the form:
(x2+4)(x−1)17x+118=x2+4Ax+B+x−1C
Step 3: Solve for the constants A, B, and C.
Multiply both sides by (x2+4)(x−1) to clear the denominators:
17x+118=(Ax+B)(x−1)+C(x2+4)
Expand the right side:
17x+118=Ax2−Ax+Bx−B+Cx2+4C
Group terms by powers of x:
17x+118=(A+C)x2+(−A+B)x+(−B+4C)
Equate the coefficients of corresponding powers of x on both sides:
For x2: A+C=0(∗1)
For x: −A+B=17(∗2)
For constant: −B+4C=118(∗3)
From (∗1), A=−C. Substitute this into (∗2):
−(−C)+B=17⟹C+B=17⟹B=17−C.
Substitute B=17−C into (∗3):
−(17−C)+4C=118
−17+C+4C=118
5C=118+17
5C=135
C=5135=27
Now find A and B:
A=−C=−27.
B=17−C=17−27=−10.
So the partial fraction decomposition is:
x2+4−27x−10+x−127
Step 4: Integrate each term.
∫(x2+4−27x−10+x−127)dx=∫x2+4−27xdx−∫x2+410dx+∫x−127dx
For the first integral, ∫x2+4−27xdx:
Let u=x2+4, then du=2xdx, so xdx=21du.
∫u−27(21du)=−227∫u1du=−227ln∣u∣=−227ln(x2+4)
(Since x2+4 is always positive, we can remove the absolute value.)
For the second integral, ∫x2+410dx:
This is of the form ∫x2+a21dx=a1arctan(ax). Here a2=4, so a=2.
10∫x2+221dx=10⋅21arctan(2x)=5arctan(2x)
For the third integral, ∫x−127dx:
27∫x−11dx=27ln∣x−1∣
Step 5: Combine the results.
−227ln(x2+4)−5arctan(2x)+27ln∣x−1∣+C
The final answer is −227ln(x2+4)−5arctan(2x)+27ln∣x−1∣+C.
What's next? Send 'em! 📸