Solve this:
Q). In the adjoining figure AB = AC and DEF is an equilateral triangle. Then

(A) a + b + c = 180
(B) a + b = 2c
(C) $a=\frac{b+c}{2}$
(D) a + c = 2b

 a . IN A EQUILATERAL TRIANGLE ALL ANGLES ARE 180 DEGREE 
          THERE FORE A+ B + C =180

b. SINCE  ABC IS A EQULATERAL TRIANGLE   ANGLE A = ANGLE B =ANGLE C 
THEREFORE a+b=2c 
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c. and d.             same as B 

Here's the answer...