Which equation combines with the given equation to form a system of equations with the solution x = 3 and y = 9? x + 2y = 21

x + 2y = 21

Step-by-step explanation:

Even other options have not been given in this question, But we will prove that equation that combines to form a system of equations is x + 2y = 21

For this we will prove this equation true for x = 3 and y = 9

x + 2y = 21

3 + 2×9 = 21

3 + 18 = 21

21 = 21

Therefore, equation x + 2y = 21 combines to form a system of equations.

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

two? xd

step-by-step explanation: