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# trigo problem?

If cos(A+B) = -0.09 and cos(A-B) = 0.85,

find (cosA * cosB) .

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- 8 months agoFavorite Answer
cos(a + b) = cos(a)cos(b) - sin(a)sin(b)

cos(a - b) = cos(a)cos(b) + sin(a)sin(b)

cos(a + b) + cos(a - b) =>

cos(a)cos(b) - sin(a)sin(b) + cos(a)cos(b) + sin(a)sin(b) =>

2 * cos(a) * cos(b) + 0 * sin(a) * sin(b) =>

2 * cos(a) * cos(b)

cos(a + b) + cos(a - b) = 2 * cos(a) * cos(b)

-0.09 + 0.85 = 2 * cos(a) * cos(b)

0.76 = 2 * cos(a) * cos(b)

0.38 = cos(a) * cos(b)

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- ComoLv 78 months ago
:-

cos A cos B - sin A sin B = - 0•09

cos A cos B + sin A sin B = 0•85________add

2 cos A cos B = 0•76

cos A cos B = 0•38

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