Cho a/b=c/d.Chứng minh ac/bd=a²+c²/b²+d²

Đáp án:

`a/b=c/d => a^2/b^2=c^2/d^2=(a^2+c^2)/(b^2+d^2)`

`a/b=c/d =(a.c)/(b.d)`

`=>(a.c)/(b.d)=(a^2+c^2)/(b^2+d^2)`