Question

Giúp mình với ạ

Answer 1

(a+b+c+d)(a-b-c+d)=(a-b+c-d)(a+b-c-d)

=>\(\left(a+d\right)^2-\left(b+c\right)^2=\left(a-d\right)^2-\left(b-c\right)^2\)

=>\(\left(a+d\right)^2-\left(a-d\right)^2=\left(b+c\right)^2-\left(b-c\right)^2\)

=>\(\left(a+d-a+d\right)\left(a+d+a-d\right)=\left(b+c-b+c\right)\left(b+c+b-c\right)\)

=>\(2d\cdot2a=2c\cdot2b\)

=>4ad=4bc

=>ad=bc

=>\(\frac{a}{c}=\frac{b}{d}\)