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8m
comment solve $\sum_{k=0}^a\binom{2a}{k}k$
@user130806, Write $k^2=k(k-1)+k$
46m
answered solve $\sum_{k=0}^a\binom{2a}{k}k$
1h
revised Proving that $\frac{\phi^{400}+1}{\phi^{200}}$ is an integer.
added 225 characters in body
1h
comment How can we find the smallest number n such that 2^(2^n) + 1 is not a prime.
en.wikipedia.org/wiki/Fermat_number#Primality_of_Fermat_numbers
2h
comment This is question about integration. I want you to check error.
See sosmath.com/tables/integral/integ11/integ11.html
2h
answered Find point on a line, given the line equation and distance from the origin
2h
comment Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
@Mickey, Here is another method
2h
answered Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
2h
comment Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
@Mickey, $$(1-\cos\theta)^2(1+\cos\theta)=(1-\cos\theta)(1-\cos\theta)(1+\cos\theta)$$ $$=(1-\cos\theta)(1-\cos^2\theta)=(1-\cos\theta)\sin^2\theta$$
2h
comment Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
@Mickey, $$(1-\cosθ)(1+\cosθ)=\sin^2\theta$$ $$\implies\sqrt{(1-\cosθ)(1+\cosθ)}=|\sin\theta|$$
2h
comment Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
@Mickey, I've started where you left of
2h
answered Find the first derivative $y=\sqrt\frac{1+\cosθ}{1-\cosθ}$
2h
comment Help solving a recursion function T(n) = T(n-2) +3
@SteveJessop, Thanks for your observation. Rectified
2h
revised Help solving a recursion function T(n) = T(n-2) +3
edited body
2h
comment Evaluating $\lim_{x \to 0}\frac{4^{\arccos^2 \frac{1}{1 + x^2}} - 1}{\log_4(1 + x)}$
@rubik, End may not always sanctify the means:) mathworld.wolfram.com/AnomalousCancellation.html
2h
revised Evaluating $\lim_{x \to 0}\frac{4^{\arccos^2 \frac{1}{1 + x^2}} - 1}{\log_4(1 + x)}$
added 41 characters in body
4h
answered Prove that $2^x+1$ is always greater or less than $3^\frac{x}{2}$?
4h
comment Trigo Problem : Find the value of $\sin\frac{2\pi}{7}+\sin\frac{4\pi}{7}+\sin\frac{8\pi}{7}$
@HimanshuArora, How about this?
4h
answered Trigo Problem : Find the value of $\sin\frac{2\pi}{7}+\sin\frac{4\pi}{7}+\sin\frac{8\pi}{7}$
5h
comment Evaluating $\lim_{x \to 0}\frac{4^{\arccos^2 \frac{1}{1 + x^2}} - 1}{\log_4(1 + x)}$
@rubik, Not sure about your area of confusion