sin^4a+2sin^2a*cos^2a+cos^4a-1= (sin^2a+cos^2a)^2 - 1 = 1^2 - 1 = 0
y=x²-4x+5=(x-2)²-4+5=(x-2)²+1
(x-2)²≥0
x-2=0, x=2
y(2)=1
Otvet: 1