Question

[Nguyễn Bá Tú]

Cho tỉ lệ thức a/b=c/d CMR :

a) \(\frac{7a+8b}{7a-8b}=\frac{7c+8d}{7c-8d}\)

b) \(\frac{11a-5b}{3a+4b}=\frac{11c-5d}{3c+4d}\)

c) \(\frac{a.b}{c.d}=\frac{a^2-b^2}{c^2-d^2}\)

d) \(\frac{\left(a+b\right)^2}{\left(c+d\right)^2}=\frac{a^2+b^2}{c^2+d^2}\)

e) \(\frac{ab}{cd}=\frac{\left(a-b\right)^2}{\left(c-d\right)^2}\)

help me 3 l-i-k-e