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Math Help - sina*cosa=4/7 , a=?

  1. #1
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    sina*cosa=4/7 , a=?

    sina*cosa=4/7 , a=?
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  2. #2
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    \sin{a} \cos{a} = \frac{4}{7}

    2\sin{a} \cos{a} = 2 \cdot \frac{4}{7}

    \sin(2a) = \frac{8}{7}

    there is no solution for "a" to satisfy this equation ... why?
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  3. #3
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    answer

    sin2a<1 then 2sina.cosa<1 so sina.cosa<1/2
    4/7 is not less than 1/2 and equation is not true.
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  4. #4
    Senior Member pacman's Avatar
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    sin 2A

    see the graph . . . . no roots possible; sin A cos A = 4/7. The red and blue wont meet . . . .



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