To make a letter the subject, undo the operations around it in reverse order. For F = 9C/5 + 32, subtract 32: F − 32 = 9C/5. Multiply by 5: 5(F − 32) = 9C. Divide by 9: C = 5(F − 32)/9.
If the letter is inside a bracket, like s = ½(u + v)t, clear the fraction and the other factors first: 2s = (u + v)t, then 2s/t = u + v, then u = 2s/t − v.
Worked example
Make m the subject of y = mx + c
- Subtract c: y − c = mx.
- Divide by x.
Answer:m = (y − c)/x
Key words
- subject
- the letter on its own
- inverse operation
- an operation that undoes another
- formula
- an equation linking quantities
Practise this
New questions every time.
Common Core-referenced: HSA-CED.A.4