changing the subject

When changing the subject, we rearrange the equation so a specific variable becomes the subject of the equation. This means the variable will appear by itself on the left-hand side of the equation.

For example, imagine that a question asks us to make the variable y the subject of the equation 4x = 6z – 2y.

• To begin with, add 2y to each side.
  The equation will change to 4x + 2y = 6z.
• Then, subtract 4x from each side of the equation.
  The equation will change to 2y = 6z – 4x.
• Lastly, divide each term in the equation by 2.
  The equation will change to y = 3z – 2x.

Now, the variable y can be seen by itself on the left-hand side of the equation, and so we can say that y is the subject of the equation.