Question

3х в квадрате + 6х = 8х в квадрате -15х

Answer 1

$3x ^{2} + 6x = 8x ^{2} - 15x \\ 3x - 8x ^{2} = - 15x - 6x \\ - 5x ^{2} = - 21x \\ 5x ^{2} - 21x = 0 \\ x(5x - 21) = 0 \\ x = 0 \\ x = 4.2$
Ответ: x=0; x=4,2