Question

A set of equations is given below:

Equation S: y = x + 9
Equation T: y = 2x + 1

Which of the following steps can be used to find the solution to the set of equations?

x=2x+1
x+9=2x
x+1=2x+9
x+9=2x+1

Answer 1

We simply equate the y.

y = x + 9 ,    y = 2x + 1

Therefore:

y = x + 9 = 2x + 1

x + 9 = 2x + 1.

The answer is the fourth option.

Answer 2

x+9=2x+1 

Since both equations give the value of y, therefor y = y. You simply substitute y with its corresponding equation.

y = y
x + 9 = 2x + 1     *we need to find the value of x to get the value of y.
x - 2x = 1 - 9
-x = -8
-1x/-1 = -8/-1
x = 8

Substitute x with its value to get y.
Equation S: y = x + 9 ⇒ y = 8 + 9 ⇒ y = 17
Equation T: y = 2x + 1 ⇒ y = 2(8) + 1 ⇒ y = 16 + 1 ⇒ y = 17 

x+9=2x+1
17 = 17