sin(a-b) =1/3,cosasinb=1/6,求cos(2a+2b)
时间: 2024-04-06 13:33:33 浏览: 215
根据三角函数的公式,有:
sin(a-b) = sinacosb - cosasinb
代入已知的值,得到:
1/3 = sin(a-b) = sinacosb - cosasinb = sin(a)cos(b) - cos(a)sin(b) = sin(a-b)
进一步化简得到:
3sin(a)cos(b) - 3cos(a)sin(b) = 1
除以3得到:
sin(a)cos(b) - cos(a)sin(b) = 1/3
根据三角函数的公式,有:
cos(2a+2b) = cos^2(a+b) - sin^2(a+b) = (cos(a)cos(b) - sin(a)sin(b))^2 - (sin(a)cos(b) + cos(a)sin(b))^2
代入已知的值,得到:
cos(2a+2b) = (cos(a)cos(b) - sin(a)sin(b))^2 - (1/3)^2 = cos^2(a)cos^2(b) - 2sin(a)cos(a)sin(b)cos(b) + sin^2(a)sin^2(b) - 1/9
化简得到:
cos(2a+2b) = cos^2(a)cos^2(b) - sin^2(a)sin^2(b) - 2/9
根据已知的条件,有:
cos(a)sin(b) = 1/6
除以cos(a)cos(b),得到:
tan(a) = 1/6cos(b)
代入sin^2(a) + cos^2(a) = 1,得到:
sin^2(a) = 1 - 1/36cos^2(b)
同理,根据已知的条件,有:
sin(a)cos(b) = 1/3
除以sin(a)sin(b),得到:
cot(b) = 3cos(a)
代入cos^2(a) + sin^2(a) = 1,得到:
cos^2(a) = 1 - 9cot^2(b)
代入cos(2a+2b)的式子,得到:
cos(2a+2b) = (1-9cot^2(b))cos^2(b) - (1-1/36cos^2(b))sin^2(b) - 2/9
化简得到:
cos(2a+2b) = (36cos^4(b) - 9cos^2(b) + 1) / (36cos^2(b) - 1)
将cosasinb=1/6代入,得到:
cos(b)sin(a) = 1/6
化简得到:
cos^2(b) - sin^2(b) = 1/36
代入cos(2a+2b)的式子,得到:
cos(2a+2b) = (4/3) / (11/36) = 16/11
因此,cos(2a+2b)的值为16/11。
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