Sum $\cos x + \cos 2x + \cdots + \cos (n-1)x.$
117200
Evaluation of $ \sum_{k=0}^n \cos k\theta $
143365
Is $\sum_{i=1}^{n-1}i=\binom{n}{2}$?
5080
How can we sum up $\sin$ and $\cos$ series when the angles are in arithmetic progression?
14386
Proof of an equality involving cosine $\sqrt{2 + \sqrt{2 + \cdots + \sqrt{2 + \sqrt{2}}}}\ =\ 2\cos (\pi/2^{n+1})$
12414
prove that : $\cos x \cdot \cos(x-60^{\circ}) \cdot \cos(x+60^{\circ})= \frac14 \cos3x$
69045
Solving this summation: $\sum_{i=1}^k i\cdot2^i$
156720
Evaluate $\sum_ {n=1}^{\infty} \cot^{-1}(2n^2)$
138172
Find the sum to n terms of the series $\frac{1}{1.2.3}+\frac{3}{2.3.4}+\frac{5}{3.4.5}+\frac{7}{4.5.6}+\cdots$..
153409
Sum of $1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}+\frac{1}{9}+\frac{1}{12}+\cdots$
49028
Find the sum : $\frac{1}{\cos0^\circ\cos1^\circ}+\frac{1}{\cos1^\circ \cos2^\circ} +\frac{1}{\cos2^\circ \cos3^\circ}+......+$
126105
Compute $\sum_{k=1}^{n} \frac 1 {k(k + 1)} $
57780
$\sum_{i=1}^n i\cdot i! = (n+1)!-1$ By Induction
138847
Tricky trigonometric sum evaluation
94060
Sum of square binomial coefficients
112005
Showing that if $p_1 + \cdots p_n = 1$ then $\displaystyle \sum_{k=1}^n \left(p_k + \dfrac {1}{p_k} \right)^2 \ge n^3+2n+\dfrac 1n$?
12812
Sum of the alternating harmonic series $\sum_{k=1}^{\infty}\frac{(-1)^{k+1}}{k} = \frac{1}{1} - \frac{1}{2} + \cdots $
83332
Trig sum: $\tan ^21^\circ+\tan ^22^\circ+\cdots+\tan^2 89^\circ = \text{?}$