cos(π/2+Q)=1/3 着 cos(π-2Q)=?
1个回答
cos(π/2+Q) = cos(-π/2-Q) = -cos(π/2-Q) = -1/3
cos(π-2Q) = 2cos^2(π/2-Q)-1 = 2 * (-1/3)^2 -1 = -7/9
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