In the figure, RGHN is a trapezium and triangles RNL and LRK are isosceles triangles. PF, PH and FH are straight lines. RN = RL = LK. Find
- ∠n
- ∠p
(a)
∠GRK = 180° - ∠n (Interior angles, RG//PH)
∠LKR = 180° - ∠n (Angles on a straight line)
∠LRK = 180° - ∠n (Isosceles triangle)
55° + 180° - ∠n + 180° - ∠n + ∠p + 19° = 180° (Angles on a straight line, FP)
55° + 180° + 180° + 19° - ∠n - ∠n + ∠p = 180°
434° - 2∠n + ∠p = 180°
2∠n - ∠p = 434° - 180°
2∠n - ∠p = 254°
∠p = 2∠n - 254° --- (1)
∠RLN
= ∠RNL
= 2 x (180° - ∠n)
= 360° - 2∠n (Exterior angle of a triangle)
∠p = 180° - (360° - 2∠n) - (360° - 2∠n)
∠p = 180° - 360° + 2∠n - 360° + 2∠n
∠p = 180° - 360° - 360° + 2∠n + 2∠n
∠p = 4∠n - 540° (Angles sum of triangle)
∠p = 4∠n - 540° --- (2)
(2) = (1)
4∠n - 540° = 2∠n - 254°
4∠n - 2∠n= 540° - 254°
2∠n = 286°
∠n
= 286° ÷ 2
= 143°
(b)
From (1)
∠p
= 2∠n - 254°
= 286° - 254°
= 32°
Answer(s): (a) 143°; (b) 32°