What is 64% of 50, work it out
2 answers:
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<h3>Answer: (x,y) = (-2, 5)</h3>
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Explanation:
4x-3y = -23 is the same as 12x-9y = -69 when we multiply both sides by 3
-3x-2y = -4 is the same as -12x-8y = -16 when we multiply both sides by 4
Our updated system looks like this
Notice how we have 12x and -12x. They combine to 0x allowing the x terms to go away.
The y terms combine to -9y+(-8y) = -17y and the right hand sides combine to -69+(-16) = -85
After doing those three sets of additions, we get the new equation -17y = -101 which solves to y = -85/(-17) = 5
The last step is to use this y value to find x
4x-3y = -23
4x-3(5) = -23
4x-15 = -23
4x = -23+15
4x = -8
x = -8/4
x = -2
So the solution is (x,y) = (-2, 5)
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Check:
Let's plug the solution into the first equation
4x-3y = -23
4(-2)-3(5) = -23
-8-15 = -23
-23 = -23
We get a true result. Let's do the same for the second equation
-3x-2y = -4
-3(-2) - 2(5) = -4
6 - 10 = -4
-4 = -4
This result is true as well. So we've confirmed both equations to fully confirm the solution of this system.
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Comments:
We can see that as long as we add/subtract any value to both sides nothing happens: true statements remain true and false statements remain false. But if we multiply or divide by negative values, false statements become true and true statements become false. That why, when you multiply or divide an inequality by a negative number, you should also flip the inequality sign. For example, if we start with the true inequality
If we multiply both sides by -2 we have to flip the sign as well:
And the inequality will remain true.