Best Math books or apps for adults to learn math from the beginning

Just create an account at KhanAcademy.org, this site is so amazing that it'll guide you from the very beggining to calculus and multivariable calculus (if you want to). It's totally free, and it will change your life. There are more than 5.000 videos. I used it and I aproove (i've watched more than 1000 yet lol). Also, they have exercises for all videos.

I've heard good things about Khan Academy. Never used it though. Also, Google is cool for finding help, since there are usually videos on Youtube to explain stuff.

Seeking proof for the formula relating Pi with its convergents

Prove $\int_0^{\pi/2}{\frac{1+2\cos 2x\cdot\ln\tan x}{1+\tan^{2\sqrt{2}} x}}\tan^{1/\sqrt{2}} x~dx=0$

Why does $\int_1^\sqrt2 \frac{1}{x}\ln\left(\frac{2-2x^2+x^4}{2x-2x^2+x^3}\right)dx$ equal to $0$?

Feeding real or even complex numbers to the integer partition function $p(n)$?

Gosper's unusual formula connecting $e$ and $\pi$

Sudoku with special properties

Why are vector spaces sometimes called linear spaces?

When L'Hôpital's Rule Fails

Has anyone found a "pattern" in prime numbers?

Finding every $n$ such that $a_n$ is an integer

Finding $n$ points $x_i$ in the plane, with $\sum_{i=1}^n \vert x_i \vert^2=1$, minimizing $\sum_{i\neq j}^n \frac{1}{\sqrt{\vert x_i-x_j \vert}}$

How does one generally find a joint distribution function (or density) from marginals when there is dependence?