This gives an interesting challenge in which students develop their understanding of functions and skills at approximation and estimation.
Students should be encouraged to try out function evaluation for various choices of numbers. Remember, that the key point is whether the function is positive or negative: we don't need to evaluate the exact values. Students should be encouraged to focus on whether the function is positive or negative, rather than computing the exact values.
What do we know about the values of a function either side of a solution?
Can you think of functions for which this sort of approach might not work?
Does this method tell us anything about the number of roots of an equation?
Note that at university this sort of idea is extended in courses on Analysis, and this result is called the Intermediate Value Theorem. It is actually a very useful and powerful mathematical idea.
Suggest that students try key values of $0.5, 1, 1.5$ and so on. Give them calculators.Suggest that they tabulate the results of their calculations.