Since I know that $\sin(4t) = 4\cos^3t\sin t-4\cos t\sin^3t$ and $\sin(3t) = 3\sin t-4\sin^3 t$ (or at least I think I do), I think I'm halfway there.
Asked
Active
Viewed 46 times
1 Answers
2
$$\dfrac{x}{4} = \sin4t \hspace{1cm}\text{and}\hspace{1cm}\dfrac{y}{3} = \sin 3t\\ \implies \sin12t = 3\left(\dfrac{x}{4}\right)-4\left(\dfrac{x}{4}\right)^3$$ using $\sin(3\theta) = 3\sin\theta-4\sin^3\theta$ and $$\sin 12t = \pm4\left(\dfrac{y}{3}\right)\dfrac{\sqrt{3-y^2}}{3}\left(1-2\left(\dfrac{y^2}{9}\right)\right)$$ using $\sin(4\theta) = 4\sin\theta\cos\theta(1-2\sin^2\theta)$
Now, equate the square of the two expressions and get the desired equation (need to square to avoid sign ambiguity of square root in the second equation).
Martund
- 14,706
- 2
- 13
- 30
-
Thanks a bunch! I knew I had to square something to get the trig identity that sums to 1, but wasn't sure how to use that in this context. Your explanation was very clear. – Austen Clark Mar 09 '20 at 14:33
-
You're welcome, @Austen. – Martund Mar 09 '20 at 14:38