Question

In a triangle abc, ab = ac, angle a = 100 degrees, then find angle abc. Select one:
a. 50 degrees
b. None of these
c. 40 degrees
d. 60 degrees

Answer 1

Answer:

C) 40°

Step-by-step explanation:

We know that angles opposite to equal sides are equal.

Sum of all angles in triangle = 180°

∠A + ∠B + ∠C = 180

100° + ∠B + ∠B = 180

=> 2∠B = 180 - 100 = 80

=> ∠B = 40°

Answer 2

Answer:  c.40 degrees

Step-by-step explanation:

ab=ac

therefore, abc is an isosceles triangle

thus, angle abc=angle acb

angle bac=100 degrees

let angle abc=angle acb=x degrees

hence,

angle abc+angle bac+angle acb=180(sum of all the angles of a triangle)

x+100+x=180

2x=180-100

2x=80

x=80/2

x=40 degrees

now,

angle abc=x=40 degrees