Question

高一数学三角函数。

f(cosx)=cos2x,则f(sin15°)= ?

Answer 1

f(cosx) = cos2x = 2(cosx)^2-1
=> f(x) = 2x^2 -1
f(sin15°)= 2(sin15°)^2 -1
= -(1-2(sin15°)^2)
= - cos30°
=-√3/2希望能帮到你 望采纳

Answer 2

解：∵ f(cosx)=cos2x=2cos²x-1
∴ f(x)=2x²-1
∴ f(sin15°)=2sin²15°-1=2（1-cos²15°）-1=1-2cos²15°
=-cos30°
=- √3/2

Answer 3

f(cosx)=cos2x=2(cosx)^2-1
所以f(x)=2x^2-1
所以f(sinπ/12)=2(sinπ/12)^2-1=-cosπ/6=-√3/2

Answer 4

cos2x=2cosx^2-1
∴f(x)=2x^2-1
∴f(sin15°)=2（sin15°）^2-1
=2[sin(45°-30°)]^2-1
=2[sin45°cos30°-cos45°sin30°]^2-1
具体结果自己算

Answer 5

sin15=cos75,所以f(sin15)=f(cos75)=cos(150)=-√3/2