Question

The three planes given meet at a point. The planes are 3x+y-2z = 11, 4x-2y+z = -5, x+5y-4z = 33. The intersection is at what point? (Please explain.)

Answer 1

Answer:

(2, 7, 1)

Step-by-step explanation:

We have three equations, and using Gauss-Jordan Elimination, we can solve for x, y, and z

3x + y - 2z = 11

4x - 2y + z = -5

x + 5y - 4z = 33

We can start by taking out the z from all rows except one. To do this, we can work with the second row. I chose the second row because -5 is small and easy to add up with other numbers, and z has no coefficient in this row.

We can add 2 times the second row to the first row and 4 times the second row to the third row to get

11x - 3y = 1

4x - 2y + z = -5

17x -3y = 13

We then have the first and third rows having two variables. Since the y coefficients are the same, we can eliminate the y by adding the negative of the first row to the third row. Our result is then

11x - 3y = 1

4x - 2y + z = -5

6x = 12

From the third row, we can gather that x= 2. We can then plug that into the first row to get

22 -3y = 1

subtract 22 from both sides

-3y = -21

divide both sides by -3

y = 7

We can then plug our x and y values into the second row to get

4(2) - 2(7) + z = -5

8 - 14 + z = -5

-6 + z = -5

add 6 to both sides

z = 1

Our answer is thus (2, 7, 1)