sin(π/2+α)=1/3,则cos(π+2α) 的值
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sin(π/2+α)=1/3,则cos(π+2α) 的值
sin(π/2+α)=1/3,则cos(π+2α) 的值
sin(π/2+α)=1/3,则cos(π+2α) 的值
根据倍角公式:
cos2x = 1 - 2sin²x
因此:
cos(π+2a) = 1 - 2sin²(π/2 + a) = 1 - 2×(1/3)²
=7/9
九分之七