Which is a difference of cubes?

x6 – 27
x15 – 36
x16 – 64
x5 – 125

Identify an equation in point slope form for the line perpendicular to y=3x+5 that passes through (4,-1)

The product of (7x-2) and (20-3x)/4. when x=4

Random variables x poisson~ ( a) ,y poisson ~ ( a) . x and y are independent. if 2 1, 2 1. u =2x+ y-1, v=2x- y +1. find: ) cov (u ,v ).