Brush up your maths: answer to algebraic expressions exercise

What would the expression 3x + 7 be when x = 3? Simplify 5x² + 7x – 2(x² + x).

When x = 3, 3x + 7 = 3 × 3 + 7 = 9 + 7 = 16.

5x² + 7x – 2(x² + x) = 5x² + 7x – 2x² – 2x = (5 – 2)x² + (7 – 2)x = 3x² + 5x = x(3x + 5)

First we check the bracket. That cannot be simplified. We multiply the contents of the brackets by the number 2. Note that the minus sign applies to both terms that we get from this. Next we collect together like terms. Finally, we take out the common factor x.

Back to question.

To Martin Bland's M.Sc. index.

To Martin Bland's home page.

This page maintained by Martin Bland.
Last updated: 2 October, 2007.

Back to top.