we need to multiply both parts of each bracket by the both parts of the other bracket: we have 2 brackets with 2 parts each, so we will have 4 expressions now:
xx; -5x; 4x; -20
now we add them:
xx+( -5x)+ 4x+( -20) - this is the expanded expression.
Now, let's simplify:
xx-5x+ 4x -20=
xx-x -20=
\(x^{2} -x-20\)