The distributive law says that:
a(b + c) = ab + ac
Example 1:
2x(4x - 1) = 8x2 - 2x
Example 2:
5x -x(4x - 1) = 5x - 1x(4x - 1) = 5x - 4x2 + 1x = -4x2 + 6x