Question
Evalute $: \left(\frac{2 x}{7}-\frac{7 y}{4}\right)^2$
✓
Answer
$\left(\frac{2 x}{7}-\frac{7 y}{4}\right)^2$
We know that
$(a-b)^2=a^2-2 a b+b^2$
$\therefore\left(\frac{2 x}{7}-\frac{7 y}{4}\right)^2$
$=\left(\frac{2 x}{7}\right)^2+\left(\frac{7 y}{4}\right)^2-2 \times \frac{2 x}{7} \times \frac{7 y}{4}$
$ =\frac{4 x^2}{49}+\frac{49 y^2}{16}-x y$
We know that
$(a-b)^2=a^2-2 a b+b^2$
$\therefore\left(\frac{2 x}{7}-\frac{7 y}{4}\right)^2$
$=\left(\frac{2 x}{7}\right)^2+\left(\frac{7 y}{4}\right)^2-2 \times \frac{2 x}{7} \times \frac{7 y}{4}$
$ =\frac{4 x^2}{49}+\frac{49 y^2}{16}-x y$
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