# Thread: sina*cosa=4/7 , a=?

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

sina*cosa=4/7 , a=?

2. $\sin{a} \cos{a} = \frac{4}{7}$

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

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

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

3. ## 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.

4. ## sin 2A

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

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