Chapter 2, Problem 18CR

To determine

To identify: Name of definition or theorem that justify the statement.

Explanation of Solution

Given:

If $\overrightarrow{NM}\perp \overrightarrow{GH}$ , then $\angle MNK=\angle MNH$

From the figure,

As, $\overrightarrow{NM}\perp \overrightarrow{GH}$

So, $\angle MNH=90$

And $\angle MNK=\angle MNH$

As perpendicular lines make an angle of 90 degrees.

So, here definition of perpendicular lines is used.