# Maths - Triangles in a Co-ordinate System

> Source: https://ollybritton.com/notes/a-level/maths/topics/triangles-coordinate-systems/ · Updated: 2020-09-21 · Tags: maths, school, year-1

##### When working with triangles in a co-ordinate system, the most important step is??
Drawing a sketch.

##### How can you prove that a triangle is right-angled in a co-ordinate system??
Find the gradients of the lines and prove two are perpindicular.

##### How can you prove two lines are perpindicular??
Show their gradients multiply to give $-1$.

##### How can you prove that a triangle is isoceles in a co-ordinate system??
Show _two_ lines have the same length.

##### What step is often forgotten in proving a triangle is isceles in a co-ordinate system??
Not showing that there is at least one length different from the other two, otherwise it would be equilateral.

##### What does the notation $|AB|$ represent in terms of co-ordinate systems??
The length of line $AB$.

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