Question

4x2 + 9y2 = 72 2x - y = 4 Which of the following is a solution to the system shown?

Answer 1

If you would like to solve the system of equations, you can do this using the following steps:

4x^2 + 9y^2 = 72
2x - y = 4 ... 2x - 4 = y
_________
4x^2 + 9y^2 = 72
4x^2 + 9 * (2x - 4)^2 = 72
4x^2 + 9 * (4x^2 - 16x + 16) = 72
4x^2 + 36x^2 - 144x + 144 = 72
40x^2 - 144x + 144 - 72 = 0
40x^2 - 144x + 72 = 0
10x^2 - 36x + 18 = 0
5x^2 - 18x + 9 = 0
(5x - 3) * (x - 3) = 0
1. 5x - 3 = 0 ... 5x = 3 ... x = 3/5
2. x = 3

1. y = 2x - 4 = 2 * 3/5 - 4 = 6/5 - 20/5 = -14/5
2. y = 2x - 4 = 2 * 3 - 4 = 6 - 4 = 2

1. (x, y) = (3/5, -14/5)
2. (x, y) = (3, 2)

The correct result would be (3/5, -14/5) and (3, 2).