sina*cosa=4/7 , a=?

**i.s.tzortzis** · October 29th 2008, 12:59 PM

sina*cosa=4/7 , a=?

**skeeter** · October 29th 2008, 01:42 PM

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

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

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

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

**afsaneh** · February 2nd 2010, 09:54 PM

sin2a<1 then 2sina.cosa<1 so sina.cosa<1/2
4/7 is not less than 1/2 and equation is not true.

**pacman** · February 2nd 2010, 10:50 PM

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

!

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sina*cosa=4/7 , a=?

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sin 2A

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