
How to change the subject of a formula.
Theory:A formula is an equation which specifies how a number of variables are related to one another. Formulas are written so that a single variable, the subject of the formula, is on the left hand side of the equation. Everything else goes on the right hand side of the equation. For example, in the formula: v = u + at , ‘v’ is the subject. Formulas are used to calculate the value of the subject when values of all of the other variables are known. To find ‘v’ in the
example, you must substitute values for ‘u’, ‘a’, and ‘t’ in the
right hand side of the equation, then evaluate. The answer will equal ‘v’. To find unknown values of ‘u’, ‘a’, or ‘t’, you can make any
of these other variables the subject, instead of ‘v’.
The following steps can be used to
change the subject of this formula: v
= u + at (1) make ‘u’ the subject of the formula:According to the order convention, beginning with ‘u’, you add ‘at’ to get ‘v’. The inverse operation is then to subtract ‘at’: ·Â Â Â Â Â Subtract ‘at’ from both sides: v

at = u + at 
at · Â Â Â Simplify: v

at = u ·Â Â Â Â Swap sides so the subject is on the left hand side: uÂ =Â v 
at (2) make ‘t’ the subject of the formula:According to the order convention, beginning with ‘t’, you multiply by ‘a’ first, then add ‘u’ to get ‘v’.Â The inverse operations are to subtract ‘u’ first, then divide by ‘a’.Â Â Â Â Â Â Â Â ·Â Â Â Â Â Subtract ‘u’ from both sides: v

u = u + at 
u ·Â Â Â Â Simplify: v

u = at ·Â Â Â Â Divide both sides by 'a': (v 
u)¸a
= at¸a ·Â Â Â Â Simplify: (v 
u)¸a
= t ·Â Â Â Â Swap sides so the subject is on the left hand side:Â t = (v
 u)¸a
Method:IMPORTANT: This topic assumes that you know how to enter mathematical formulas into Algematics. Find out how by completing the three simple tutorials in the 'Getting Started' section of the Algematics program 'Help'. We will use the example described in the ‘theory’ section above to demonstrate how to change the subject of a formula using Algematics.Â We will use Algematics to make ‘u’ the subject of the formula: v = u + at Step 1Â Enter the dataClick
Â and
type the original formula into the maths box in the data entry dialog box. If
the ‘EMPTY’ message is not displayed between the blue buttons, click the
Â button
until the message: ‘INSERT’ appears.Â If
necessary, use the ' * ' symbol for multiply and the ' / ' symbol for divide. Â Â Â Â Â Â
Maths... Â
Â v
= u + at Â Â Â and then click Step 2 Apply inverse operations to isolate the new subjectÂRepeat steps 'a', 'b' and 'c' below until all inverse operations have been performed...
NOTE: Click the
Â (swap) button if the
subject has ended up Â
