Calculate expression: $\cos\alpha-\cos2\alpha$
90226
Proving trigonometric equation $\cos(36^\circ) - \cos(72^\circ) = 1/2$
100907
$\sin\alpha + \sin\beta + \sin\gamma = 4\cos{\frac{\alpha}{2}}\cos{\frac{\beta}{2}}\cos{\frac{\gamma}{2}}$ when $\alpha + \beta + \gamma = \pi$
42391
Calculate $\tan9^{\circ}-\tan27^{\circ}-\tan63^{\circ}+\tan81^{\circ}$
97984
Express as sum of powers
68881
Solve for $\theta$: $a = b\tan\theta - \frac{c}{\cos\theta}$
59045
Expression under summation on multiple lines
5747
$\cos(\arcsin(x)) = \sqrt{1 - x^2}$. How?
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
104321
Prove that $1 + \cos\alpha + \cos\beta + \cos\gamma = 0$
51787
Evaluate $\int \cos(3x) \sin(2x) \, dx$.
571
How to evaluate a math expression given in string form?
27628
Solving $a \sin\theta + b \cos\theta = c$
1317
Combining cosine or sine terms into a single cosine or sine
118408
Equation with cos and product
121617
Closed form of $\sum_{n=0}^{\infty} \frac{\cos(\alpha \, n)}{n!}$
84433
Expression generating $\left( \frac{3}{10}, \, \frac{3}{10} + \frac{33}{100}, \, \frac{3}{10} + \frac{33}{100} + \frac{333}{1000}, \dots \right)$
40556
Why is $\sin(\alpha+\beta)=\sin\alpha\cos\beta+\sin\beta\cos\alpha$