I know, you might say I'm stupid because I don't know this, but I'm stuck.

I need to know how to do this :

(x + y)²

Would it be something like :

x² + (2 x xy) + y²

x² + xy² + y²

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The thing is though, I know how to do this :

(5 + x)²

= 25 + (2 x 5x) + x²

= 25 + 10x + x²

Seeeee ^^

I know how to do the ones with a letter and number, but I don't know how to do the ones with two letters.