Let $x = \sin10^\circ$. The formula for $\sin3\theta$ shows that $3x - 4x^3 = \sin30^\circ = \frac12.$ So $8x^3 - 6x + 1 = 0.$ If $y=2x$ then $y^3 -...
Sometimes editing a thread title is an issue, but the issue is with vBulletin. If you ever want to change a thread title, and can't, just let me know...
Perhaps there are differences in terminology...I was taught that a function is concave up on an interval when its second derivative is positive, and...
No the link was meant to be HTTPS. I was thinking that you might have the HTTP site bookmarked and could be posting through that somehow but honestly...
Well, I don't know about rigorous, but intuitively if you're talking about the limit as $h\to 0$, then $h\not=0$, which forces $\|h\|\not=0$ (in most...