cos(x-pai/4)=根号2/10,x属于(pai/2,3pai/4)求sinx和sin(2x+pai/3)

问题描述:

cos(x-pai/4)=根号2/10,x属于(pai/2,3pai/4)求sinx和sin(2x+pai/3)

cos(x-π/4)=cosxcosπ/4+sinxsinπ/4=√2/2*(cosx+sinx)=√2/10sinx+cosx=1/5cosx=1/5-sinx平方cos²x=1-sin²x=1/25-2/5*sinx+sin²xsin²x-1/5*sinx-12/25=0(sinx-4/5)(sinx+3/5)=0由x范围sinx>0...