sin²a+cos²a=1
所以sina=4√3/7
同理sin(a+b)=5√3/14
cosb=cos(a+b-a)
=cos(a+b)cosa+sin(a+b)sina
=-17/98
問(wèn)一個(gè)三角函數(shù)的題
問(wèn)一個(gè)三角函數(shù)的題
a,b都是銳角cos a = 1/7 cos(a+b) = -11/14 求cos b
a,b都是銳角cos a = 1/7 cos(a+b) = -11/14 求cos b
數(shù)學(xué)人氣：698 ℃時(shí)間：2020-06-13 01:55:52
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