JAMB - Mathematics (1980 - No. 22)
A pentagon has four of its angles equal. If the size of the fifth angle is 60o, Find the size of each of the four equal angles.
60o
108o
120o
150o
None of the above
Wyjaśnienie
The sum of interior angle of pentagon
(5 sides) = (2n - 4) x 90o
n = 5
(2 x 5 - 4) x 90o = 6 x 90o
= 540o
540o - 60o = 480o \(\div\) 4
= 120o
(5 sides) = (2n - 4) x 90o
n = 5
(2 x 5 - 4) x 90o = 6 x 90o
= 540o
540o - 60o = 480o \(\div\) 4
= 120o