Review question

# Can we calculate an approximation to the root of this function? Add to your resource collection Remove from your resource collection Add notes to this resource View your notes for this resource

Ref: R5948

## Suggestion

It is known that the equation $f(x) = 0$ has only one real root in the interval $a < x < b$ and that $f(a) < 0$, $f(b) > 0$. The two points $A$ and $B$ lie on the graph of $f(x)$ and have coordinates $(a,f(a))$ and $(b,f(b))$ respectively. By finding where the line $AB$ cuts the axis of $x$, show that $\begin{equation*} \frac{af(b) - bf(a)}{f(b) - f(a)} \end{equation*}$

is an approximation to the root.

How could we find where the line $AB$ cuts the $x$-axis?

You may find the resource In-betweens helpful here.