Marcus wants to exchange his American dollars to pesos before leaving on a trip to Mexico. A bank offers 13 pesos for each American dollar. The bank charges a service fee of $2.50
to exchange the money. Which equation models the number of pesos, y, that Marcus will
receive for x American dollars after the service fee?

i think the length is 12 and the width is 17

(5x-1)^2= (5x)^2-2(5x)×1+(1)^2=25x^2-10x+1

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