1题设角a终边上一点P(x,y)
|OP|=r=√(x²+y²)
sina=y/r,cosa=x/r ,tana=y/x
所以 sin²a+cos²a=(x²+y²)/r²=1
sina/cosa=(y/r)/(x/r)=y/x=tana 2题 1-cos^6α-sin^6α)/(1-cos^4α-sin^4α)
1=sin^2α+cos^2α
原式=(sin^2α+cos^2α-cos^6α-sin^6α) /(sin^2α+cos^2α-cos^4α-sin^4α)
分母=sin^2α(1-sin^2α)+cos^2α(1-cos^2α)=2sin^2αcos^2α
分子=sin^2α(1-sin^4α)+cos^2α(1-cos^4α)
sin^2α(1-sin^4α)=sin^2α(1-sin^2α)(1+sin^2α)=sin^2αcos^2α(1+sin^2α)
同理cos^2α(1-cos^4α)=sin^2αcos^2α(1+cos^2α)
原式=sin^2αcos^2α(1+sin^2α+1+cos^2α)/2sin^2αcos^2α=3/2