Question

2. In A ABC (fig. 11.39), side BC is produced to B BA D. If ABC = 40° and ACD = 120° find ZA.​

Answer 1

Answer:

∵AB=AC⇒∠ABC=∠ACB=x(say)

Let ∠BAC=y

We know,

Exterior angles = sun of interior opposite angles

or, 120

o

=∠ABC+∠BAC

or, 120

o

=x+y−−−(1)

Again, ∠ACB+∠ACD=180

o

or, x+120

o

=180

o

∴

x=60

o

From (1),

60

o

+y=120

o

⇒

y=60

o

∴

∠A=60

o

Answer 2

Angle ACD + angle ACB = 180 (liners pair)

120 + angle ACB = 180

Angle ACB = 60

Angle A + B + C =180

A + 40 + 60 = 180

A + 100 = 180

Angle A = 80