(sina+cosa)/sinacosa=4/3令y=sina+cosax=sinacosa则y²=sin²a+cos²a+2sinacosa=1+2xy/x=4/3y²/x²=16/9所以(1+2x)/x²=16/916x²-18x-9=0x=3/2,x=-3/8sin2a=2x由sin值域sin2a=-3/4...