Project ForgeGeneral Aptitude
Quantitative Aptitude
GATE 2020
Medium
Two straight lines are drawn perpendicular to each other in the X-Y plane. If α and β are the acute angles the straight lines make with the X-axis, then α + β is _____.
- A60°
- 90°
- C120°
- D180°
Explanation
If one line makes angle θ (0°<θ<90°) with the x-axis, a line perpendicular to it makes an angle of θ+90° with the x-axis — but the ACUTE angle that perpendicular line forms with the x-axis is its supplement-reduced value, 90°−θ (which stays between 0° and 90° automatically). So α=θ and β=90°−θ, giving α+β = 90° regardless of θ.
Source: GATE CS 2020 (2020)
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