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An expression is a mixture of numbers, letters and symbols (+, - , · …) that doesn’t include the “=“ symbol.

      3x-5        (a+b)2


To substitute in an expression is to put numbers instead of letters.


The value of an expression is the answer you get after substituting numbers for letters:

                         The value of 3x+5 is 14 if x = 3


Exercise: Find an algebraic expression for these sentences:

a) The double of a number plus five.

b) The double of a number, plus five.

c) Half a number minus eight.

d) The square of the double of a number.



Solutions: a) 2·(x + 5); b) 2x + 5; c) (x-8)/2; d) (2x)2