Question

Уравнение:

$x^{2} = 21 -7x^{2}$

Answer 1

$8x^{2} =21$
$x^{2} = frac{21}{8}$
$x=+- sqrt{ frac{21}{8} } =+- sqrt{ frac{21}{4*2} } =+- frac{1}{2} sqrt{ frac{21}{2} }$

Answer 2

исправила