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GATE 2020 CS – Question 9

General Aptitude · Quantitative Aptitude: Algebra, Geometry and Mensuration · 2 marks · Multiple choice

Two straight lines are drawn perpendicular to each other in X-Y plane. If $\alpha$ and $\beta$ are the acute angles the straight lines make with the X-axis, then $\alpha+\beta$ is ______.

  1. $60^\circ$
  2. $90^\circ$
  3. $120^\circ$
  4. $180^\circ$

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Show answer and explanation

Correct answer: (B) $90^\circ$

Explanation

If one line makes angle $\alpha$ with the X-axis, the perpendicular line makes $90^\circ-\alpha$ as its acute angle. So $\alpha+\beta=90^\circ$.