Question

34. In A ABC, if BC = AB and angle b = 80°, then angle a
is equal to
(a) 40° (6) 50° (c) 60° 1 (d) 70°​

Answer 1

Answer:

50

Step-by-step explanation:

abc is an isoscles triangle  

by isosceles triangle thm

angle a = Angle c   ....(1)

in abc

a + b + c = 180

angle addition prop. of a triangle

a + 80 +a = 180    from (1)

2a + 80 = 180

2a = 100

a = 50

Answer 2

In triangle Abc

BC=AB

Therefore by a theorem which states that

'Angles opposite to equal sides are equal'

/_A=/_C

angle a+b+c=180(Angle sum property)

a+a+b=180 (a=c)

2a+b=180

2a+80=180

2a=180-80

2a=100

a=100/2

a=50

Therefore a=c=50

${50}^{.}$