Formulae Substitution and Rearranging Formulae Substituting into Formulae
Formulae Substitution and Rearranging
Formulae
Substituting into Formulae The process of substitution is replacing a variable with a number. Once the variables have been replaced with the numerical values, you then simplify. Example Find the volume of a cuboid, which has length 2 m, width 1 m, and height of 1. 5 m We know that the V = lwh V = 2⨯ 1⨯ 1. 5 V = 3 m 3 Formulae expression Substitute values Final answer (don’t forget units if appropriate)
Changing the subject of a formulae What would happen if you encountered the following scenario? The volume of a cuboid is 2400 cm 3, and you know the length is 20 cm, and the width is 12 cm. What is the height? Writing it out gives us V = lwh 2400 = 20⨯ 12⨯h What is h? - We could guess? - Or we could rearrange our formula to make the unknown variable (h) to be on the left hand side h = ? ? ? - This is called making ‘h’ the subject of the formula.
Changing the subject of a formulae This means rearranging the formula to put the variable of interest on the left hand side. How do we do this? ? - move numbers and variables from one side of the equation to the other - follow algebra convention rules on keeping the equation balanced by doing the reverse operation when changing sides Ø Multiply on one side, becomes division on the other side Ø Addition on one side, becomes subtraction on the other side Ø Squared on one side, becomes square root on the other side
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