Hi, I am not a student but am reviewing calculus for an upcoming interview. I would like to know how to derive the area of a triangle using calculus. Thanks!

Todd Bowie

Hi Todd,

Using calculus to calculate any area involves integration. Remember that the integral of the difference between two curves gives you the area between those curves, that is

where f(x) lies above g(x), is the area enclosed by f(x) and g(x) between the points x=a and x=b.

Now, a triangle is made up of three lines connecting the three vertices. To find the area between these three lines, you must find their equations and integrate their differences. Here's a quick (and simple) example:

To find the area of the triangle with vertices (0,0), (1,1) and (2,0), first draw a graph of that triangle. It is made up of the three lines y=0, y=x, and y=2-x. Now look at your graph:

Between the points x=0 and x=1 (i.e. the left half of the triangle) we want to find the area between y=x and y=0. For the right half of the triangle we need to find the area between y=2-x and y=0. Hence we compute:

Area = A(left) + A(right)

which is

The value of which is 1 square unit.

The most important thing is to always draw a picture first and use it to figure out what the equations of your lines are and in how many parts you need to split the triangle to compute the area.

Good luck on the interview,

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