If the largest angle in a triangle is 75°, what is the least possible value of the smallest angle of the triangle?
- AOption (a)
76°
- BOption (b)
70°
- COption (c)
30°
- DOption (d)
40°
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Correct answer
30°
Why this answer is correct
Shortcut Trick In a triangle, to minimize the smallest angle, the other two angles must be as large as possible. Given the largest angle is 75°, the second-largest angle can at most be 75°. Least possible smallest angle = 180° − (Largest Angle + Max possible second angle) Least possible smallest angle = 180° − (75° + 75°) = 180° − 150° = 30°. ∴ The correct answer is 30°. Alternate Method Given: The largest angle of the triangle is 75°. Formula Used: The sum of all interior angles of a triangle is always 180°.
Calculations: ⇒ Let the three angles of the triangle be x, y, and z. ⇒ According to the question, let the largest angle z = 75°. ⇒ By the Angle Sum Property: x + y + z = 180° ⇒ x + y + 75° = 180° ⇒ x + y = 180° − 75° = 105° ⇒ To find the least possible value of the smallest angle (x), we must maximize the second angle (y). ⇒ Since 75° is the maximum angle, y cannot exceed 75°. So, the maximum value of y = 75°. ⇒ Least value of x = 105° − 75° = 30°. ∴ The correct answer is 30°. Additional Information Angle Sum Property The sum of the three interior angles of any Euclidean triangle is always 180°. Types of Triangles by Angles Acute (all angles < 90°), Right (one angle = 90°), and Obtuse (one angle > 90°). Isosceles Triangle Property In this problem, the minimum value occurs when the triangle is isosceles with two angles equal to 75°.
