(1) 题目不全,怀疑是:求证sin^4(t)+cos^4(t)+2sin^2(t)cos^2(t)=1 成立.
证:sin^4(t)+cos^4(t)+2sin^2(t)cos^2(t)
=[sin^2(t)+cos^2(t)]^2
=1^2
=1
(2) 后一个题目也不对,估计是:已知sinx=0.1,x∈(π/2,π),求cos2x,tan(x+π/4)
∵sinx=0.1 x∈(π/2,π)
∴ cosx=-√(1-0.1^2)=-0.9950
tanx=-0.1/0.9950=0.1005
cos2x=1-2sin^2(x)=1-2*0.1^2=0.9800
tan(x+π/4)=[tanx+tan(π/4)]/[1-tanx*tan(π/4)]
=(0.1005+1)/(1-0.1005)=1.2235