Solve for theta

**jewd777** · April 21st 2009, 07:12 PM

25sin@ -1.5 cos@ = 20 @ = theta

**Chris L T521** · April 21st 2009, 09:04 PM

Originally Posted by jewd777

25 sin@ -1.5 cos@ = 20, whats @ = ?

Hint: Apply the identity $A\cos\theta+B\sin\theta=\sqrt{A^2+B^2}\cos\!\left( x-\tan^{-1}\!\left(\tfrac{B}{A}\right)\right)$

**Calculus26** · April 21st 2009, 10:29 PM

there may be a more clever way but by brute force and ignorance:
Solve for 25 sin(@) = 20+1.5cos(@)

square both sides and convert the LHS to a fn of cos(@)

you now have a quadratic in cos@

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