化简cos(-210°)乘tan(-120°)+sin240°乘cos150°h结果是
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化简cos(-210°)乘tan(-120°)+sin240°乘cos150°h结果是
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cos(-210°) = cos210° = cos(180°+30°) = - cos30° = - √3 /2
tan(-120°) = tan(60° - 180°) = tan60° = √3
sin240° = sin(180°+60°) = - sin60° = - √3 /2
cos150° = cos(180° - 30°) = - cos30° = - √3 /2
原式 = - √3 /2 *√3 +(-√3 /2)*(-√3 /2)
= - 3/2 + 3/4
= - 3/4
cos(-210°) = cos210° = cos(180°+30°) = - cos30° = - √3 /2
tan(-120°) = tan(60° - 180°) = tan60° = √3
sin240° = sin(180°+60°) = - sin60° = - √3 /2
cos150° = cos(180° - 30°) = - cos30° = - √3 /2
原式 = - √3 /2 *√3 +(-√3 /2)*(-√3 /2)
= - 3/2 + 3/4
= - 3/4
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