If $\dfrac{a}{b} = \dfrac{c}{d}$, then $\dfrac{(a-b)(c-d)}{(a+b)(c+d)}$ equals—

Question

Accepted Answer

$\left(\dfrac{a-b}{a+b}\right)^2$

Answer

$\dfrac{a-b}{a+b}$

Answer

$1$

Answer

$0$

If ab=cd\dfrac{a}{b} = \dfrac{c}{d}ba​=dc​, then (a−b)(c−d)(a+b)(c+d)\dfrac{(a-b)(c-d)}{(a+b)(c+d)}(a+b)(c+d)(a−b)(c−d)​ equals—