Which is an example of the associative property?

a.

3 • (x + 5) = 3 • x + 15

b.

x + 5 = 5 + x

c.

(x + 3) + 7 = x + (3 + 7)

d.

if x = a, and a = 7, then x = 7.

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