trigo problem?

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

find (cosA * cosB) . 

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    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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  • Como
    Lv 7
    8 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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  • Fuhr
    Lv 6
    8 months ago

    Seven               .

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