The notation PR ⊥ NP tells us that lines PR and NP are perpendicular. This means they create a 90^(∘) angle between them. Let's mark these lines with blue in our figure.
We see that NP is a vertical line. For any line to be perpendicular with a vertical line, it would have to be horizontal. Since PR is not a horizontal line, it cannot be perpendicular with NP.
