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E2. Using formulae
Change the subject of an equation

In the equation y=5x-4, y is said to be the subject of the equation. In each of the following equations, the letter in red is the subject of the equation: t=4w², x=4(y+7), w=u+½vt The subject of an equation can be changed to any of the other letters present in it by using the rules of algebra. An example Make x the subject of y=3x-8 Write down the equation y=3x-8 Add 8 to both sides: y+8=3x Divide both sides by 3: (y+8)/3=x Thus x=(y+8)/3 Another example Make w the subject of t=2w-4 Write down the equation  t=2w - 4 Add 4 to both sides: t + 4=2w Divide both sides by 2: (t + 4)/2=w Thus w=(t + 4)/2 Yet another example Make v the subject of u=v²+7 Write down the equation u=v²+7 Subtract 7 from both sides: u-7=v² Take the square root of both sides: Ö(u-7)=v Thus v=Ö(u-7)

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