Higher November 2017 Paper 3 Q26
26 \(a^2 - b^2 \equiv (a + b)(a - b)\)
\(a\) and \(b\) are positive whole numbers with \(a \gt b\)
\(a^2 - b^2\) is a prime number.
Why are \(a\) and \(b\) consecutive numbers? [2 marks]
| Answer | Mark | Comments |
|---|---|---|
| Full explanation stating one of \(a + b\) or \(a - b\) must be 1 and \(a + b\) cannot be 1 and \(a - b\) must be 1 | B2 | B1 partial explanation ie \(a + b\) or \(a - b\) must be 1 or \(a + b\) cannot be 1 or \(a - b\) must be 1 |