Sign up ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Write the equation:


In the form:


I have to fill in the blank spot. Any help?

share|cite|improve this question

2 Answers 2

up vote 2 down vote accepted

Hint: if $\theta = \tan^{-1}(19/13)$, $\cos(\theta) = 13/ R$ and $\sin(\theta) = 19/ R$ for some $R$. What is $R$? Note that $\sin(\theta) \sin(13 t/8) + \cos(\theta) \cos(13t/8) = \cos(13 t/8 - \theta)$.

share|cite|improve this answer


$$a \sin(\theta) + b \cos(\theta) = \sqrt{a^2 + b^2} \times \cos(\theta - \arctan(a/b))$$

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.