There are mnemonic acronyms out there for reminding you how to do this. I think of it simply as using the distributive property. (4x-3)(x+5) = 4x(x+5) -3(x+5) then again = (4x² +20x) + (-3x -15) = 4x² + (20-3)x -15 . . . . . . . combine like terms = 4x² +17x -15