The lines $y = x$ and $y = -x$ in the plane, with direction vectors $(1, 1)$ and $(1, -1)$

Example · High school

Terms

Term	This example	Why
right angle	✓	The lines $y = x$ and $y = -x$ cross at the origin and form four right angles there.
perpendicular	✓	The lines $y = x$ and $y = -x$ are perpendicular, because the lines intersect at the origin and the product of their slopes is $1 \cdot (-1) = -1$.
orthogonal	✓	The direction vectors $(1, 1)$ and $(1, -1)$ of the lines $y = x$ and $y = -x$ are orthogonal, because their dot product is $1 - 1 = 0$.

Distinctions using this example

• Right angle vs. perpendicular vs. orthogonal vs. normal

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