If two lines are perpendicular, then they form:

A cross because they are intersecting each other at the center of each line.

If two lines are perpendicular, they form a 90° angle, or a right angle. By definition, two perpendicular lines intersect at a right angle. For instance, a vertical line and a horizontal line will cross at a 90° angle.

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Here is a (very crude) sketch of two perpendicular lines. The box between the place where the lines intersect indicates a right angle.

Hope this helps!

She should use 12/3 to measure