## ewkmath 2 years ago what is X when 2sin^2(X)+9cos(X)+3=0

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have you subbed $$\sin^2 x x = 1-\cos^2 x$$ into the eq to simplify it into a quadratic eq?

2. ewkmath

no i haven't but i'll try it out right now thanks :)

u r welcome. The solution should be trivial after the substitution. :)

4. ewkmath

I tried it but i still don't get it..

subbing, you should get, $$2-2\cos^2 x + 9 \cos x +3=0$$ which equals, $$-2\cos^2 x + 9 \cos x +5=0$$ let u = cos x the equation becomes $$-2u^2 + 9 u +5=0$$ which is a quadratic equation of u. You can use the general formula to solve for u.

6. ewkmath

thanks o much.. i really appreciate it