To split in to partial fractions, the expression

Jaylyn Villarreal

Jaylyn Villarreal

Answered question

2022-04-09

To split in to partial fractions, the expression 1x2(x+a)2
1x2(x+a)2=Ax+Bx2+C(x+a)+D(x+a)2
One method of finding the values of the constants A,B,C  &  D is as follows.
Ax(x+a)2+B(x+a)2+C(x2)(x+a)+Dx2=1
Ax(x2+a2+2ax)+B(x2+2ax+a2)+C(x3+ax2)+Dx2=1
A(x3+a2x+2ax2)+B(x2+2ax+a2)+C(x3+ax2)+Dx2=1
x3(A+C)+x2(2Aa+B+Ca+D)+x(Aa2+2Ba)+Ba2=1
Equating coeffecients of x3,x2,x1,x0
A+C=0,2Aa+B+Ca+D=0,Aa2+2Ba=0,Ba2=1
B=1a2
A=2a3
C=2a3
D=1a2
Is there a shorter method to find the values of A,B,C & D ?

Answer & Explanation

muthe2ulj

muthe2ulj

Beginner2022-04-10Added 10 answers

Ax(x+a)2+B(x+a)2+C(x2)(x+a)+Dx2=1
x=0 yields b=1a2
x=a yields d=1a2
Then you can derivate and set again x=a and x=0 to get A,C or replace B,D in that equation to get
Ax(x+a)2+C(x2)(x+a)+2x2a2+2axa2+1=1
After canceling the 1's, you can divide by x(x+a) and get
A(x+a)+Cx+2a2=0
x=0 yields A=2a3
and x=a yields C=2a3
tutaonana223a

tutaonana223a

Beginner2022-04-11Added 15 answers

In this equation:
Ax(x+a)2+B(x+a)2+C(x2)(x+a)+Dx2=1
one little thing you can do is to evaluate at x=a to get
0+0+0+D(a)2=1 to get D. After that can evaluate at x=0 to get B.

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