Solve the system by method of choice (addition or substitution)

Question

x²+2y²=324

x+y=18

Answer 1

Substitution method : 

Given equations are

  ---> (1)

x + y  = 18       ---> (2)

solve for y from (2).

Subtract y from each side.

x = 18 - y         ---> (3)

Substitue x = 18 - y in (1).

.

Substitute in (3)

x = 18 - 12 = 6.

Solution  x = 6 and y = 12.

 

Comments

please check your answer,
y^2 - 12y = 0
y(y-12) = 0
y = 0 and y = 12.
If y = 0 then x = 18 - y => x = 18.
If y = 12 then x = 18 - y => x = 18 - 12 = 6.
The two ordered-pair solutions are (x, y) = (6, 12) and (x, y) = (18, 0).