解r=√(-3)²+(-4)²=√25=5∴sina=y/r=-4/5∴cosa=x/r=-3/5∴sin2a=2sinacosa=2×(-4/5)(-3/5)=24/25∴cos2a=2cos²a-1=2×(-3/5)²-1=18/25-1=-7/25∴cos(2a+π/4)=√2/2cos2a-√2/2sin2a=√2/2(-...