Question

3x^2-15=0, x^2+7x=0, 12x^2-5x-2=0

Answer 1

$3 {x}^{2} - 15 = 0 \ {x}^{2} - 5 = 0 \ x = + - sqrt{5}$

${x}^{2} + 7x = 0 \ x(x + 7) = 0 \ x = 0 \ x = - 7$

$12 {x}^{2} - 5x - 2 = 0$
D = 25+96=121
$x = frac{5 + 11}{2 times 12 } = frac{2}{3} \ x = frac{5 - 11}{2 times 12} = - frac{1}{4}$