Hey everyone.

I've recently joined KhanaAcademy. While watching https://www.khanacademy.org/math/algebra2/x2ec2f6f830c9fb89:poly-arithmetic/x2ec2f6f830c9fb89:poly-add-sub/v/subtracting-polynomials?modal=1. teacher has mention -1 multiplies with negative turns positive.

My question is when we multiply one positive number and one negative number becomes negative, positive * positive becomes positive, but when we multiply two negative numbers how they goes in positive side or number line?