y=sin(派分之四+x)乘以cos(派分之四+x)=1/6 x属于(90,180)求cos2s和sin4x的值

问题描述:

y=sin(派分之四+x)乘以cos(派分之四+x)=1/6 x属于(90,180)求cos2s和sin4x的值

sin(π/4+x)=(√2/2)cosx+(√2/2)sinx=(√2/2)(cosx+sinx)cos(π/4+x)=(√2/2)cosx-(√2/2)sinx=(√2/2)(cosx-sinx)∴原式=(√2/2)(√2/2)(cosx-sinx)(cosx+sinx)=[(cosx)^2-(sinx)^2]/2=(cos2x)/2 =1/6∴cos2x=1/3x...