sin(π/2+α)·cos(π/2-α)/cos(π+α)+sin(π-α)·cos(π/2+α)/sin(π+α)=?(2)sin²40°+sin²50°=?(3)已知sin10°=k,则cos620°=?(4)已知f(cosx)=cos3x,则f(cos30°)=?
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/27 22:16:00
![sin(π/2+α)·cos(π/2-α)/cos(π+α)+sin(π-α)·cos(π/2+α)/sin(π+α)=?(2)sin²40°+sin²50°=?(3)已知sin10°=k,则cos620°=?(4)已知f(cosx)=cos3x,则f(cos30°)=?](/uploads/image/z/8553391-7-1.jpg?t=sin%28%CF%80%2F2%2B%CE%B1%29%C2%B7cos%28%CF%80%2F2-%CE%B1%29%2Fcos%28%CF%80%2B%CE%B1%29%2Bsin%EF%BC%88%CF%80-%CE%B1%EF%BC%89%C2%B7cos%EF%BC%88%CF%80%2F2%2B%CE%B1%EF%BC%89%2Fsin%EF%BC%88%CF%80%2B%CE%B1%EF%BC%89%3D%3F%EF%BC%882%EF%BC%89sin%26%23178%3B40%C2%B0%2Bsin%26%23178%3B50%C2%B0%3D%3F%EF%BC%883%EF%BC%89%E5%B7%B2%E7%9F%A5sin10%C2%B0%3Dk%2C%E5%88%99cos620%C2%B0%3D%3F%EF%BC%884%EF%BC%89%E5%B7%B2%E7%9F%A5f%EF%BC%88cosx%EF%BC%89%3Dcos3x%2C%E5%88%99f%EF%BC%88cos30%C2%B0%EF%BC%89%3D%3F)
sin(π/2+α)·cos(π/2-α)/cos(π+α)+sin(π-α)·cos(π/2+α)/sin(π+α)=?(2)sin²40°+sin²50°=?(3)已知sin10°=k,则cos620°=?(4)已知f(cosx)=cos3x,则f(cos30°)=?
sin(π/2+α)·cos(π/2-α)/cos(π+α)+sin(π-α)·cos(π/2+α)/sin(π+α)=?
(2)sin²40°+sin²50°=?
(3)已知sin10°=k,则cos620°=?
(4)已知f(cosx)=cos3x,则f(cos30°)=?
sin(π/2+α)·cos(π/2-α)/cos(π+α)+sin(π-α)·cos(π/2+α)/sin(π+α)=?(2)sin²40°+sin²50°=?(3)已知sin10°=k,则cos620°=?(4)已知f(cosx)=cos3x,则f(cos30°)=?
=cosα*sinα/(-cosα)+sinα*(-sinα)/-sinα
=-sinα+sinα
=0
第二题继续啊 ,先占座
(2)sin²40°+sin²50°=sin²40°+cos²40°=1
(3)已知sin10°=k,则cos620°=cos(620°-720°)=cos(-80°)=cos80°=sin10°=k
(4)已知f(cosx)=cos3x,则f(cos30°)=X
第四题,稍等片刻
cos3x=cos(2x+x)=cos2xcosx-sin2xsinx=(2cos^2x-1)cosx-2sinx cosx sinx
=(2cos^2x-1)cosx-2sinx sinx cosx
=(2cos^2x-1)cosx-2(1-cos^2 x)cosx=2cos^3x-cosx+2cos^2x-2
即f(cosx)=2cos^3x-cosx+2cos^2x-2
即f(x)=2x^3+2x^2-x-2
把x=cos3x带入得
f(cos30°)=2(cos30°)^3-cos30°+2(cos30°)^2-2
=2*(根号3/2)3-根号3/2+2*3/4-2
剩下的,你自己化简吧 打字实在不容易 写字快