How do you solve x = y + 3 and 2x + y = 9 using substitution?

1 Answer
Jarni Renz
Mar 14, 2016

You are given 2 variables, decide which variable you want to be substituted and what equation will be your base equation to plug in your value.

Explanation:

1, In this case, 2x + y =9 may be use as your base equation and x=y+3, since this equation does not need rearrangement to find the value of x, will be used to substitute (for x from your base equation) to find the value of y;
2. From your base equation, substitute the value of x;
2color(red)x +y=9; where x=y+3 forming like this
2color(red)((y+3))+y=9
3. Now, as reflected above, you have only one variable and you can now find the value y;
4. Then simplify the equation and combine like terms if applicable until you can arrive the value of y;
2(y+3)+y=9
2y +6+y=9
3y+6=9
5. Isolate the term with y from the numerical value by subtracting 6 both sides of the equation;
6. The value of y = 1
7. To find the value of x, you can use either of the equations and plug in the value of y;
8. Always remember to plug in values of y and x to check if both sides of the 2 equations are balanced.

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