化简4(sinα)^2+2sinαcosα-1

1个回答

4(sinα)^2+2sinαcosα-1
= -2[1-2(Sina)^2]+ sin2a+1
= -2cos2a+sin2a+1
参考公式Cos2a=1-2Sin^2(a) sin2A=2sinA·cosA