For your job, you need to order 25 packages of copy paper for the printer. A local office supply store sells the paper for $8.95 per package, plus 5% sales tax. An online company sells the paper for $11.95 per package and offers a rebate of 10% for the whole order, with no additional sales tax. If you choose the better of the two prices, how much will you pay for the 25 packages of paper?

x^2 + 81

we can factor this using difference of square binomials.

rewrite the equation:

x^2 - (-81)

factor:

(a^2 - b^2) = (√a^2 + √b^2)(√a^2 - √b^2)

(x^2 - (-81) = (x + √-81)(x - √-81)

we can remove the - from under the radical by multiplying it by i.

(x^2 - (-81) = (x + i√81)(x - i√81)

(x^2 - (-81) = (x + 9i)(x - 9i)

we can check our answer by using foil:

x^2 - 9ix + 9ix - 81i^2

x^2 - 81^2

i^2 = -1

x^2 + 81