Factor the expression. 49b^2 – 36

a. (7b – 6)(7b – 6)

b. (7b 6)(7b 6)

c. (6b 7)(6b – 7)

d. (7b 6)(7b – 6)

Aclassmate thinks that solving a system by graphing gives an exact answer when the lines appear to cross at a grid point, but only an approximate answer when they don't. explain why this isn't true.