А) 4b^2 - 24bc+cb-6c^2 + 23bc-3b^2= b^2 - 6с^2.
б) 10а^2 - 6а - а^2 + 4а +2а - 8= 3а^2 + 6а - 8.
в) х^2+14х+49-49+х^2=2х^2+14х.
Вот использовала формулу синус двойного угла
1)cos(3π/4-2x)=-1
sin(2x-π/4)=-1
2x-π/4=-π/4+2πn
2x=2πn
x=πn
2)ctg(π/6-x/2)=-1
tg(x/2+π/3)=-1
x/2+π/3=-π/4+πn
x=-7π/12+πn
2x^2+3x = 2x^2+21
3x = 21
x = 7
(3x+1)(4x-5) = 12x^2-13x+1
12x^2-11x-5 = 12x^2-13x+1
2x = 6
x = 3
(2x-3)(3x+7)-(x-5) = 12x^2-13x+1
6x^2+14x-9x-21-x+5 = 12x^2-13x+1
-6x^2+17x = 17
x(17-6x) = 17