已知f(1+sinx)=2+sinx+cos2x,求f(x)
1个回答

你好

解:

令u=1+sinx,则

sinx=u-1 (0≤u≤2),

cos2x=1-2sin²x=1-2(u-1)²=1-2(u²-2u+1)=1-2u²+4u-2=-2u²+4u-1

则f(u)=2+(u-1 )+(-2u²+4u-1)=-2u²+5u

不对呀

f(1+sinx)=2+sinx+cos²x

cos²x=1-sin²x=1-(u-1)²=1-u²+2u-1=-u²+2u

f(u)=2+(u-1 )+(-u2+2u) (0≤u≤2)

=2+u-1--u2+2u

=-u²+3u+1

故f(x)=-x²+3x+1 (0≤x≤2)

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