I dislike education acronyms, but I can make exceptions for mathematical ones. One of my favourite topics in A-level Maths is full to bursting with them: DRVs, CRVs, PDF, CDF. This is a visual representation of the CDF (cumulative distribution function) of a CRV (continuous random variable), which is the function for the area under the curve from *x*=-∞ to any other value, *a*, or more specifically, P(X<*a*). Take note of the syntax for piecewise functions.

The PDF (probability density function) of the CRV I’ve used* is

and its CDF is

.

But you don’t need to know the CDF to represent it in Desmos, you just need to use inequalities to shade the region between the *x*-axis and the curve, with a slider for the variable value of *x*. The syntax is a little unusual, but take a look and you’ll see how it’s done. The same principle was used in my model for normal distribution.

*It’s taken from the Edexcel S2 exam, June 2012, question 7.

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