In ?ABC above, BC is produced to D, /AB/ = /AC/ and ?BAC = 50°.

MATHEMATICS

WAEC 1995

In ?ABC above, BC is produced to D, /AB/ = /AC/ and ?BAC = 50°. Find ?ACD

A. 50°
B. 60°
C. 65°
D. 115°

Correct Answer: D. 115°

Explanation

ACB = ABC [Base angles of isoceles triangle]

ACB + ABC + 50^o = 180^o[sum of angles in a triangle]

ACB + ABC = 180^o - 50^o = 130^o

ACB

130^o/2

= 65^o

ACD + ACB = 180^o[sum of ?s on a straight line]

ACD + 65^o = 180^o

ACD = 180^o - 65^o = 115^o

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