1）sin^4x+cos^4x=5/8 求cos4x 2）sin^4x-cos^4x=-4/5求sin2x
问题描述：
1）sin^4x+cos^4x=5/8 求cos4x 2）sin^4x-cos^4x=-4/5求sin2x
要有过程越详细越好
答
1.sin^4x + cos^4x=(sin^2x+cos^2x)^2 - 2sin^2xcos^2x=5/8∵sin^2x+cos^2x=1∴1-2sin^2xcos^2x=5/82sin^2xcos^2x=3/8则：(sin2x)^2=3/4cos4x=1-2(sin2x)^2=1 - 3/2 =-1/22.∵sin^4x-cos^4x=(sin^2x+cos^2x)(sin^2x-...