Some equations cannot be solved algebraically. They can be solved by finding numerical approximations, by applying numerical methods. Numerical methods find improved approximations from existing ones.
Showing an equation has a root
For an equation , it can be shown that there is a root between and by showing that there is a sign change between and . Also, this method can be used to show the accuracy of a root, by considering the error interval of a given root.
This method only works for continuous functions. If a function has an asymptote or other discontinuity, this method does not work.