f(x)=2x^2-3x+1 x∈R 求值域

f(x)=2x²-3x+1
=2(x²-3x/2)+1
=2(x² -3x/2 +9/16) -1/8
=2(x- 3/4)² -1/8
平方项恒非负,(x- 3/4)²≥0 2(x- 3/4)²≥0 2(x- 3/4)² -1/8≥-1/8
f(x)≥-1/8,函数的值域为[-1/8,+∞).