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An angle is three times its own supplement. Find the angle.

Class 7Lines and AnglesLines and Angles
  • A135°
  • B45°
  • C67.5°
  • D90°

Step-by-Step Solution

Let the angle be , so its supplement is . Then → → → °. Check: supplement = 45°, and 3 (45) = 135. Trap: 45° is the supplement, not the angle; 67.5° is the answer to the COMPLEMENT version of the same sentence , so it shows the two words were swapped.
Answer: A) 135°

Key idea: Solving 'find the angle' problems

Most Class-7 angle problems give you one or two angle measures and ask you to find an unknown one. The recipe:

1. Identify the relationship: vertically opposite? linear pair? corresponding? alternate?
2. Write an equation: equal-to or sum-to-180.
3. Solve for the unknown.
4. Mark it back on the diagram and sanity-check (acute should look acute, obtuse should look obtuse).

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