y=4sinxcosx=2sin2x x=0,y=2sin0=0 x=π/4,y=2sinπ/2=2 x=π/2,y=2sinπ=0 x=3π/4,y=2sin3π/2=-2 y=2sin2x在[π/4,3π/4]的区间内递减,在[0,π/4]的区间内递增 π/2,6,
