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# How do you do math substitution?

Updated: 4/28/2022

Wiki User

13y ago

Mathematical substitution is the process of using one equation to solve for multiple variables. For example:

Equation 1: x + y = 4

Equation 2: 2x + y = 16

Using equation 1, solve for y:

y = 4 - x <-- Plug this into equation 2. This is substitution because you are replacing y in equation 2 with what y is equal to in equation 1.

2x + y = 16 ----> 2x + (4 - x) = 16

Now you can solve for x: x + 4 = 16; x = 12

You can then substitute the value of x back into the equation that is solved for y:

y = 4 - 12; y = -8

Check both equations:

Equation 1: -8 + 12 = 4; 4 = 4 (Correct)

Equation 2: 2(12) + (-8) = 16; 24 - 8 = 16; 16 = 16 (Correct)

We have successfully used substitution to solve for two different variables, x and y.

Wiki User

13y ago

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Q: How do you do math substitution?
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