1.3 Changing the Subject of a Formula

Question 1

What is the area of a trapezium?

Answer 1

A = 1/2(a + b)h

a and b are the lengths of the parallel sides.

Question 2

What variable should be arranged to be at the left-side of the equation?

Answer 2

The subject whose value you want to determine.

For example: if you want /a/ to be the subject in A = 1/2(a + b)h

A/h = 1/2(a + b)
2A/h = a + b
2A/h - b = a
therefore, a = 2A/h - b