Three angles of a quadrilateral

Question:

Three angles of a quadrilateral are $75^{\circ}, 90^{\circ}$ and $75^{\circ}$, then the fourth angle is

(a) $90^{\circ}$

(b) $95^{\circ}$

(c) $105^{\circ}$

(d) $120^{\circ}$

Solution:

(d) Given, ∠A = 75°, ∠B = 90° and ∠C = 75°

We know that, sum of all the1 angles of a quadrilateral is 360°.

∠A+ ∠B + ∠C + ∠D = 360°

=> 75° + 90°+ 75°+ ∠D = 360°

∠D = 360° – (75° + 90° + 75°)

= 360° -240° = 120°

Hence, the fourth angle of a quadrilateral is 120°.

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