求值：cos（x+27°）cos（x-18°）+sin（x+27°）sin（x-18°） 急救急救!

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• 求值：cos（x+27°）cos（x-18°）+sin（x+27°）sin（x-18°） 急救急救!
• cos(x+27°)cos(18°-x)-sin(18°-x)sin(x+27°)=cos(x+27°)cos(18°-x)+cos[90°-(60°-x)]sin(x-18°)
• sin(x-27°)cos(18°-x)-sin(60°-x)sin(x-18°)为啥答案给的可以化简为sin(x+27°)cos(18°-x)+cos(90°-63°+x)sin(18°-x)
• cos(x+27°)cos(18°-x)-sin(18°-x)sin(x+27°)=cos(x+27°)cos(18°-x)+cos[90°-(60°-x)]sin(x-18°)原本是-sin(18°-x)负号怎么变成的+cos[90°-(60°-x)] cos前的负号
• 求值：cos（x+27°）cos（x-18°）+sin（x+27°）sin（x-18°） 急救急救!
• tan675°+1/tan765°-sin(-5π/2)+1/cos(-23π/6)
• cos^6(π/8)-sin^6(π/8)=求值,[cos^2(π/8)-sin^2(π/8)][cos^4(π/8)+sin^4(π/8)+cos^2(π/8)sin^2(π/8)]=cos(π/4)[1-cos^2(π/8)sin^2(π/8)]=cos(π/4)[1-[sin^2(π/4)]/4]==7√2/16