cos²（π/8）-0.5=

cos²（π/8）-0.5=
cos²（π/8）-0.5=

cos²（π/8）-0.5=
cos²（π/8）-0.5
=[1+cos(2*π/8)]/2-0.5
=(1+√2/2)/2-1/2
=√2/4

cos²（π/8）=[cos（π/4﹚+1]/2=(√2+2）/4
cos²（π/8）-0.5==(√2+2）/4-1/2=√2/4cos²（π/8）=[cos（π/4﹚+1]/2是怎么得来的？公式：cos2a=cos²a-sin²a cos²a+sin²a=1 所以：cos&#...

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cos²（π/8）=[cos（π/4﹚+1]/2=(√2+2）/4
cos²（π/8）-0.5==(√2+2）/4-1/2=√2/4

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