# Tips & Challenges

## GC setting for faster graph plot

Method 1: Change Xres to 3

The Xres button refers to pixel resolution (1 through 8). At Xres = 1, functions are evaluated and graphed at each pixel on the x-axis. At Xres = 8, functions are evaluated and graphed at every eighth pixel along the x-axis. Small Xres values improve graph resolution but may cause the calculator to draw graphs more slowly. Setting Xres to 3 provides good balance between speed and resolution.

Example

Xres= 1

Time taken to plot= 23.4 s

Xres= 3

Time taken to plot= 3.6 s

Savings of almost 20 seconds! Which is crucial in exams

Method 2: Turn off “Detect Asymptotes”

## Approximation in series expansion

This question was posed by a student.

Explanation

Exact versus approximation. The two curves depart from each other at x=pi/5

When we use the approximation to compute the volume, it differs significantly from the exact volume.

## Sum and Difference of Two cubes

In 2013 alevel, factorisation of the difference of two cubes can be used in one of the questions

Here are the formulas students should remember:

Students can use the mnemonic “SOAP” to help them remember the formula.

S: Same sign

O: Opposite sign

A: Always

P: Positive