Question

39. In ∆ABC, BC = AB and ∠B = 80°. Then ∠A is equal to: a) 80o b) 40o c) 50o d) 100o​

Answer 1

Answer:

50 degree

Step-by-step explanation:

BC=AB

⇒∠A=∠C (As angles opposite to equal side are equal)

let thte angles be x each.

Now by angle sum property

∠A+∠B+∠C=180

∘

⇒x+80

∘

+x=180

∘

⇒2x=180

∘

−80

∘

⇒2x=100

∘

⇒x=50

∘

∴∠A=50

∘

Answer 2

Answer:

50°

Step-by-step explanation:

AB=AC

⇒∠A=∠C  BECAUSE equal sides have equal angle opposite to the side

⇒∠A+∠B+∠C=180

⇒∠A+∠A+∠B=180° BECAUSE ∠A=∠C

⇒∠B+2∠A=180°

⇒2∠A+80=180°

⇒2∠A=180-80=100

⇒∠A=100/2=50°

⇒∠A+1