In a previous Math-FAQ, we looked at the different parts of a parabola. Based on this information, you know that to find the x intercepts of a parabola we need to solve a quadratic equation. When we solve a quadraticÂ equation to find the x intercepts of the graph, you might expect to always have solutions. But as the Math-FAQ below shows, this is not always the case.

# Author: Dr Dave

## The Compound Interest Formula and Its Many Faces

The compound interest formula appears in many classes. It can be confusing to students when it appears in one class as

and in another as

These are basically the same formulas, but used in a different context. However, how you solve for the different quantities in either one is the same. The Math-FAQs below demonstrate how to solve forÂ

## It’s All Relative…or It’s Not

Extrema are the high and low points on a function’s graph.

It can be difficult to distinguish between the bumps and dips on a graph, the relative (or local) extrema, and the very highest and lowest points on a graph, the absolute extrema.

The Math-FAQ belows show how to find each type of extrema using derivatives.

## Calculating Rates from the Limit Definition

Students often struggle with calculating rates from the limit definition,

Because of this, there are many FAQs available to help you work through these problems.

- Math-FAQ: How do you find the instantaneous rate of change?
- Math-FAQ: What is the difference between a secant line and a tangent line?
- Math-FAQ: How do you find the equation of a tangent line?
- Math-FAQ: How do you find a derivative at a point from the definition?
- Math-FAQ: How do you find the instantaneous rate from a table?

These examples should help you to solve problems from Section 11.2 and Section 11.3.

## Another System of Linear Equations

Often the most difficult part of solving a system of equations problem is writing out the system from a word description. In this FAQ, we look at a complicated sounding problem and form a system of linear equations from the problem.

This FAQ explores how to take a story problem and write it out as a system of linear equations.