Expand and simplify (x+4)(x-5).

For this, we use the FOIL method of expanding brackets; start by multiplying the FIRST terms of each bracket together to get xx=x^2. Next multiply the OUTSIDE elements, ie the first element in the first bracket and the last in the second, giving x(-5)=-5x. Then comes the INSIDE elements, giving 4x=4x, and finaly the LAST elements of each bracket, giving 4(-5)=-20. Adding all these terms together gives us our answer; x^2+4x-5x-20, which can be simplified to x^2-x-20.