3x+5y=-9
4x+y=5 /*(-5)⇒-20x-5y=-25
прибавим
-17х=-34
х=2
8+у=5
у=5-8
у=-3
(2;-3)
2t(t+8)-(t-6)²=2t²+16t-t²+12t-36=t²+28t-36=(t+14+2√58)(t+14-2√58)
D=784+144=928
√D=4√58
t1=(-28-4√58)/2=-14-2√58 U x2=-14+2√58)
25a²-(2a-8)²
=(5a-2a+8)(5a+2a-8)=(3a+8)(7a-8)