John is building a rectangular puppy kennel up against his house using 31 feet of fencing. the side against the house does not need a fence and the side parallel to his house needs to be 15 feet long. write an equation that models the situation and solve for the length of one of the shorter sides that extend out from the house.

hello from mrbilldoesmath!

answer:

(7 x + 6 y) (49 x^2 - 42 x y + 36 y^2)

discussion:

the trick is to recognize that 343 = 7^3 and 216 = 6^3 and, in general,

a^3 + b^3 =   (a + b) (a^2 - a b + b^2).

in our case

343x^3+216y^3   =   (7x)^3 + (6y)^3

so take a = 7x and b = 6y in the above equation to get the answer.

you,

mrb

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