What am I? Series 1.3

"The difficulty is not guessing the riddle. It is to explain the riddle" anyways, let's start.

I kind of look like a heart shape when I look at the mirror. Better than looking at a mirror while suffering an extra stroke to look like my cube.

Oh yeah that one person from ancient philosphy era, thanks for powering that theoroem but I guess if u add me one more time, I became a final theoroem to another person.

But when someone, double the size of me, stands to the left of me, WE COULD ANSWER EVERYTHING.

I hope you know who I am, because I am really awesome.

You are...

The number $2$.

I kind of look like a heart shape when I look at the mirror.

The mirror image of $2$ along with it's mirror image looks like the heart shape.

Better than looking at a mirror while suffering an extra stroke to look like my cube.

An extra pen-stroke turns $2$ into $3$, which, along with it's mirror image, forms $8$, which is cube of $2$.

Oh yeah that one person from ancient philosophy era, thanks for powering that theorem....

Pythagoras' Theorem, where $2$ occurs as "powers", i.e., exponents.

I guess if u add me one more time, I became a final theorem to another person.

Fermat's Last Theorem, of course. Specifically, adding $2$ to itself gives $4$, and Fermat himself proved the case $n=4$.

But when someone, double the size of me, stands to the left of me, WE COULD ANSWER EVERYTHING.

When $4$ stands next to $2$, we get $42$, which "Answer to the Ultimate Question of Life, the Universe, and Everything"

• Exactly what I thought! Well done! – ministic2001 Jun 25 '16 at 9:39