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5x + 6y = 18 and 18x -15y =36

2 Answers

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Solution : {x,y,z} = {-3,-2,-1} System of Linear Equations entered : [1] x + 6y + 3z = -18 [2] -x + 6y - 3z = -6 [3] 5x - 6y + 3z = -6 Solve by Substitution :// Solve equation [1] for the variable x
[1] x = -6y - 3z - 18 // Plug this in for variable x in equation [2]
[2] -(-6y-3z-18) + 6y - 3z = -6 [2] 12y = -24 // Plug this in for variable x in equation [3]
[3] 5•(-6y-3z-18) - 6y + 3z = -6 [3] - 36y - 12z = 84 // Solve equation [2] for the variable y

[2] 12y = - 24 [2] y = - 2 // Plug this in for variable y in equation [3]
[3] - 36•(-2) - 12z = 84 [3] - 12z = 12 // Solve equation [3] for the variable z

[3] 12z = - 12 [3] z = - 1 // By now we know this much : x = -6y-3z-18 y = -2 z = -1// Use the y and z values to solve for x
x = -6(-2)-3(-1)-18 = -3 Solution : {x,y,z} = {-3,-2,-1} Processing ends successfully
User Jensey
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7.9k points
4 votes
5x+6y=18

5x=18-6y

x=(18-6y)/5

Use that in the other equation
18(18-6y)/5 - 15y = 36

64.8-21.6y - 15y = 36

28.8=36.6y
.7868=y

Now put that number in for y on the first equation

5x+6(.78) = 18
5x + 4.68 = 18
5x = 13.32
x = 2.66
and y = .78


User Dave Hirschfeld
by
7.6k points

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