Question 1098071
start with (4+a) * (4-a) - 12 - 3a


(4+a) * (4-a) = 16 - a^2


expression becomes 16 - a^2 - 12 - 3a


rearrange in descending order of degree to get -a^2 - 3a - 12 + 16


combine like terms to get -a^2 - 3a + 4


set this equal to 0 to get -a^2 - 3a + 4 = 0


it's easier to factor if the coefficient of the x^2 term is positive so multiply both sides of the equation by -1 to get:


a^2 + 3a - 4 = 0


factor this quadratic equation to get (a+4) * (a-1) = 0


solve for a to get a = -4 or a = 1.


you are basically simplifying it and combining like terms and you are left with a quadratic equation which you factor in the usual ways.