The two rules
A standard method from Surds: the steps and worked examples.
Steps
- √a × √b = √(ab)
- √a ÷ √b = √(a/b)
- k√a + m√a = (k + m)√a: add or subtract like surds only.
But √a + √b is not √(a + b). √9 + √16 = 7, but √25 = 5.
Worked examples
Example 1: Use the two rules: √8 × √6 and √72 ÷ √2.
√8 × √6 = √48 = √(16 × 3) = 4√3
√72 ÷ √2 = √36 = 6For the whole topic, read Surds: key points, common mistakes and how the DSE tests it.