.函数y=2sin^2x+2cosx-3的最大值是多少
y=2(1-cos^2x)+2cosx-3
=-2cos^2x+2cosx-1
=-2(cosx-1/2)^2-1/2
cosx=1/2时,Y有最大值是:-1/2.
若tanB=3,sin^2B-cos2B等于多少
sin^2B-cos2B
=sin^2B-(cos^2B-sin^2B)
=2sin^2B-cos^2B
=(2sin^2B-cos^2B)/(sin^2B+cos^2B)
=(2tan^2B-1)/(tan^2B+1)
=(2*9-1)/(9+1)
=17/10