Hoặc
c) a2+abb−a:a+b2a2−2b2;
c) a2+abb−a:a+b2a2−2b2=a(a+b)b−a:a+b2(a+b)(a−b)
=−a(a+b)a−b:12(a−b)=−2a(a+b)(a−b)a−b
= −2a(a + b) = −2a2 – 2b2.