(a-4)^2-2a(5a-4) = a^2-8a+16-10a^2+8a = -9a^2+16; при a = -1/3 -9a^2+16 = -9(-1/3)^2+16 = -9*1/9+16 = -1+16 = 15
a^2-8a+16-10a^2+8a=0
-9a^2+16=0 *(-1)
(3a-4)(3a+4)=0
a=-1/3
ответ -15
