这一步之后怎么化简的？
追答你没学过凑角公式嘛？
追问有的
追答那就是了，提一个二分之根号2
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第1个回答 2015-02-03
13. f(x)=(sinx+cosx)sinx
=sin^2x+sinxcosx
=(1-cos2x)/2+1/2*sin2x
=1/2*sin2x-1/2*cos2x+1/2
=√2(√2/2*sin2x-√2/2*cos2x)+1/2
=√2(sin2xcosπ/4-cos2xsinπ/4)+1/2
=√2sin(2x-π/4)+1/2
T=2π/2=π
-1<=sin(2x-π/4)<=1
-√2<=√2sin(2x-π/4)<=√2
1/2-√2<=√2sin(2x-π/4)+1/2<=1/2+√2
所以A=1/2-√2追问
=sin^2x+sinxcosx
=(1-cos2x)/2+1/2*sin2x
=1/2*sin2x-1/2*cos2x+1/2
=√2(√2/2*sin2x-√2/2*cos2x)+1/2
=√2(sin2xcosπ/4-cos2xsinπ/4)+1/2
=√2sin(2x-π/4)+1/2
T=2π/2=π
-1<=sin(2x-π/4)<=1
-√2<=√2sin(2x-π/4)<=√2
1/2-√2<=√2sin(2x-π/4)+1/2<=1/2+√2
所以A=1/2-√2追问
12题呢？？
追答
望采纳
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