Question:
Solve:
$\frac{2-7 x}{1-5 x}=\frac{3+7 x}{4+5 x}$
Solution:
$\frac{2-7 x}{1-5 x}=\frac{3+7 x}{4+5 x}$
$\Rightarrow(4+5 x)(2-7 x)=(1-5 x)(3+7 x)$ (by cross multiplication)
$\Rightarrow 8-28 x+10 x-35 x^{2}=3+7 x-15 x-35 x^{2}$
$\Rightarrow-35 x^{2}-18 x+8=-35 x^{2}-8 x+3$
$\Rightarrow-35 x^{2}+35 x^{2}-18 x+8 x=-8+3$
$\Rightarrow-10 x=-5$
$\Rightarrow x=\frac{-5}{-10}=\frac{1}{2}$
$\therefore x=\frac{1}{2}$