16Hit1600
Geometry and TrigonometryHardAngle between a perpendicular and a parallel line

Geometry and Trigonometry practice question

Lines l and m are parallel. A third line crosses both, making an acute angle of 35° with line l. A fourth line, perpendicular to the third line, also crosses line m. What is the measure, in degrees, of the acute angle between the fourth line and line m?

Answer: 55

The third line makes 35° with m as well, since l and m are parallel. The fourth line is at 90° to the third, so its acute angle with m is 90 − 35 = 55.

Common wrong answers

If you answered 35
35 is the third line's angle with m.
If you answered 90
90 is the angle between the third and fourth lines.
If you answered 145
145 is the obtuse angle.

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