An expresion, is a mixture of numbers, letters and symbols (+, -, ·, ...) that doesn't include the "=symbol".
3x - 5 (a+b)2
Look at these examples:
- The triple of a number: 3n
- The triple of a number minus five units: 3n-5
- The following number: x+1
- The preceding number: x-1
- An even number: 2x An odd number: 2x+1
Exercise 1: 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
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 if x = 3: 3 · 3 + 5 = 14
