Question

数学老师在线解答？

怎么做

Answer 1

y
=2(cosx)^2 +cosx -2
=2[ (cosx)^2 + (1/2)cosx + 1/16] -1/8 -2
=2(cosx +1/4)^2 - 17/8
max y = 2(1+1/4)^2 -17/8 = 25/8 -17/8 =1
min y = 0-17/8 =-17/8
y 的值域=[ -17/8, 1]