Algebraic expressions

An algebraic expression is a record made from numbers and letters joined by operation signs; a letter can stand for any number. For example, the phrase “double a number and subtract 5” is written as 2a - 5. To find the numerical value of an expression, we put the given numbers in place of the letters and carry out the operations in the usual order. When substituting a negative number, putting it in brackets prevents mistakes: in 5 - 2k with k = -4 we get 5 - 2 · (-4) = 13. If an expression contains division, we may only use values that make the divisor non-zero. Turning a text description into an algebraic expression means writing the problem in the language of mathematics.