If two angles of a triangle have measures of 42° and 20°, what is the measure of the third? A. 118° B. 98° C. 108° D. 128°
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Answer:
Step-by-step explanation:
1) ABCD is a trapezium. AB ║ CD
∠ADC + ∠DAB = 180° { Co interior angles}
110° + ∠DAB = 180
∠DAB = 180 -110
∠DAB = 70°
2) Sum of all angles of trapezium = 360°
∠A + ∠B + ∠DCB + ∠D = 360
70° + 50° + ∠DCB + 110° = 360
230 + ∠DCB = 360
∠DCB = 360 - 230
∠DCB = 130°
3) For finding the height, use Pythagorean theorem
height² + base² = hypotenuse²
height² + 6² = 10²
height² + 36 =100
height² = 100 - 36
height² = 64
height = √64
height = 8 m
4) a = AB = x m
b = 9 m
h = height = 8 m
Area of trapezium = 120 m²
= 120
x + 9 = 120/4
x + 9 = 30
x = 30 - 9
x = 21 m
AB = 21m