# Question about Basic Algebra Rules (Adding something to both sides)

I have a question about basic algebra. Ofcourse, you can add something to both sides to make the equation hold true, but where can you not?

Here for example: $10x(3)=10$ and adding 10 to both sides $10x(3+10)=20$ is not going to hold true. Is there like a list I could look at for those kinds of rules?

I'm watching a video of a teacher explaining how to solve a quadratic equation and he just casually adds something to a multiplication and the same on the other side. So I don't really understood how it's possible since on the one side we are not multiplying and on the other we do, that can't really hold the same value?

• Adding 10 to 10x(3) is 10x(3)+10! Be careful with brackets – QuIcKmAtHs Jan 5 '18 at 6:00

You have to add the same number to both sides. You added $10(10x)$ to one side and $10$ to the other side.