Note that − a = 0 − a = ( − 1)× a, and a − b = a + ( − b )
One need only think of a toddler with two operations to do, eat lunch and wash face, to realise that the order in which the operations are done makes a tremendous difference to the result.
When evaluating numerical or algebraic expressions, we need to know the order in which addition, subtraction, multiplication, division and exponents are carried out. For all numerical or algebraic expressions, the order of evaluation is ( BEDMAS ):
If an expression involves two or more operations at the same level of priority, those operations are done from left to right.
Click on the question marks to see the following examples done step-by-step. Keep the following order of operations in mind when studying these examples:
When brackets occur within brackets, solve the expression inside the inner-most brackets first.
[4 + 2(3 + 2 × 4)] ÷ 2 = [4 + 2(3 + 8)] ÷ 2 = [4 + 2(11)] ÷ 2 = [4 + 22] ÷ 2 = 26 ÷ 2 = 13
When a quotient is written as a ratio the numerator and the denominator are evaluated first. That is, we treat the numerator and denominator as if they were inside brackets. For example,
To calculate -a2, first find the square of a, a2. Then take its negative. So -a2 is the negative of a2.
To calculate (-a)2, square -a.
For example, -32 = -9. But (-3)2 = 9.
(While the above is the correct order of operations, note that
Excel evaluates -a2 as (-a)2.)
Now try some of these exercises:
If an expression involves functions such as
, ex, ln(x), sin(x) or cos(x) they have to be evaluated first, before they can be raised to a power, multiplied, divided, added or subtracted. They are given First Priority.
Now try some of these exercises. (The notation sqrt(a) is used for and exp(x) for ex.)