已知sina=-2cosa,求sin^2a+5sina*cosa+2cos^2a的值

问题描述:

已知sina=-2cosa,求sin^2a+5sina*cosa+2cos^2a的值

sina=-2cosasina+2cosa=0sin^2a+4sina*cosa+4cos^2a=01.25sin^2a+5sina*cosa+5cos^2a=0sin^2a+5sina*cosa+2cos^2a=(1.25sin^2a+5sina*cosa+5cos^2a)-0.25sin^2a-3cos^2a=-0.25sin^2a-3cos^2asina=-2cosasin^2a=4cos^...