1. Factorise the denominator and identify that the fraction is improper.
Denominator: (x−3)(x2−9)=(x−3)(x−3)(x+3)=(x−3)2(x+3)
Expanding the denominator gives x3−3x2−9x+27.
The degree of the numerator (3) is equal to the degree of the denominator (3), so it is an improper fraction.
2. Perform long division to extract the polynomial part.
2\cline2−2x3−3x2−9x+27\cline2−2\vline2x3−4x2−5x+3\vline2x3−6x2−18x+54\vline2x2+13x−51
So, (x−3)(x2−9)2x3−4x2−5x+3=2+(x−3)2(x+3)2x2+13x−51.
3. Set up the partial fraction decomposition for the proper fraction part.
Let (x−3)2(x+3)2x2+13x−51=x−3A+(x−3)2B+x+3C.
Multiplying by (x−3)2(x+3) gives:
2x2+13x−51=A(x−3)(x+3)+B(x+3)+C(x−3)2
4. Solve for the constants $A$, $B$, and $C$.
Substitute x=3:
2(3)2+13(3)−51=B(3+3)
18+39−51=6B⟹6=6B⟹B=1
Substitute x=−3:
2(−3)2+13(−3)−51=C(−3−3)2
18−39−51=36C⟹−72=36C⟹C=−2
Compare coefficients of x2:
2=A+C
2=A−2⟹A=4
5. Write the final expression.
(x−3)(x2−9)2x3−4x2−5x+3=2+x−34+(x−3)21−x+32
Answer2+x−34+(x−3)21−x+32