Question

Khai triển tích:

a.A=(a/b-b/a)(a²/b²+b²/a²+a/b.b/a)

b.B=(a/b+b/a)(a/b-b/a)

Answer 1

Đặt a/b = x ; b/a = y cho dẽ 

a) A = ( x - y )( x^2 + y^2 - xy )

        = x^3 + xy^2 - x^2y - x^2y - y^3 + xy^2

        = x^3 - y^3

        = (a/b)^3 - (b/a)^3  

Answer 2

b)\(B=\left(\frac{a}{b}+\frac{b}{a}\right).\left(\frac{a}{b}-\frac{b}{a}\right)\)

\(=>B=\frac{a}{b}^2-\frac{b}{a}^2\)

\(=>B=\frac{a^2}{b^2}-\frac{b^2}{a^2}\)

\(=>B=\frac{a^4-b^4}{a^2.b^2}\)