Question

find value of R when
√25×25+50×50+2×25×50×cos120

Answer 1

cos 120 = $-\frac{1}{2}$

$\sqrt{25 * 25 + 50 * 50 + 2 * 25 * 50 * (-\frac{1}{2})}$
$= \sqrt{(25^2 + 50^2 + 2 * 25 * 50) * (-\frac{1}{2})}$
$= \sqrt{(25 + 50)^2 * (-\frac{1}{2})}$
$= \sqrt{75^2 * (-\frac{1}{2})}$
$= 75\sqrt{-\frac{1}{2}}$

Hope this will be helpful.