2.5 Constructing and solving equations · Unit 2 Expressions, formulae and equations

1 · Teaching slidesuse ← → keys

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2 · Key words

equationNumbers and letters with an equals sign, such as x + 5 = 12.

solveTo find the value of the unknown letter.

solutionThe value of the letter that makes the equation true.

inverse operationThe operation that undoes another; used to solve equations.

balanceWhatever you do to one side of an equation you must do to the other.

3 · Summary of the sectionrevise from this

An equation is a balance: the two sides are equal.
To solve, do the same thing to both sides until the letter is alone.
Use inverse operations: undo + with −, undo × with ÷.
Undo in reverse order — deal with the + or − first, then the × or ÷.
x + 5 = 12 → subtract 5 → x = 7. 2y + 4 = 16 → subtract 4 → 2y = 12 → divide by 2 → y = 6.
With brackets you can divide by the number outside first: 4(x − 2) = 20 → x − 2 = 5 → x = 7.
Always check by substituting your solution back into the original equation.