...=а^2-7a-3a+21-6a^2+10a=-5a^2+0+21=-5a^2+21
(а+в-с)^2-(а-в+с)^2=(а+в-с-а+в-с)(а+в-с+а-в+с)=(2в-2с)2а=(в-с)4а
Решение
<span>3x^2+5x+2m=0
D = 25 - 4*3*2m = 25 - 24m
x</span>₁ = [- 5 - (25 - 24m)] / 6 = (- 30 + 24m) / 6
По условию задачи
<span>(- 30 + 24m) / 6 = - 1
</span>- 30 + 24m = - 6
24m = 24
m = 1
x₁ = <span> (- 30 + 24*1) / 6
</span>x₁ = - 1
x₂<span> = [- 5 + (25 - 24m)] / 6 = (20 - 24m) / 6
</span>x₂ = (<span>20 - 24*1) / 6
x</span>₂ = - 4/6
x₂ = - 2/3