解
最简公分母为x(x-y)(x+y)
∴
1/(x²-y²)=x/x(x²-y²)=x/x(x-y)(x+y)
1/(x²+xy)=(x-y)/x(x+y)(x-y)
最简公分母为：(m-3)(m+3)
1/(m²-9)=1/(m-3)(m+3)
1/(3+m)=(m-3)/(m+3)(m-3)
最简公分母为：(x+y)(x-y)
1/(x²-y²)=1/(x-y)(x+y)
1/(x+y)=(x-y)/(x+y)(x-y)
第一个是(1-b)(1+b)
第二个是(1+b)²
第三个是(b-1)²=(1-b)²
∴最简公分母为(1-b)²(1+b)²