Question

28 or30 ''''''''''''''''''''''''''''

Answer 1

$<b >Hey here is your answer$

$\color{green} {\mathbb{\underline{\star{ANSWER \: NO \: :- \: 28}\star}}}$

Given :-
(1) AB = AC
(2) AB = AD

To prove :- <C = 90°

Proof :-

In ∆ ABC

AB = AC (Given) -(1)
<ABC = <ACB (angle opposite to equal side of ∆ are equal) -(2)

Now ,

In figure:-
AB = AD (Given) -(3)

From (1) and (3) :-

AC = AD

Now, In ∆ ACD

AC = AD (proved above)
<ACD = <ADC -(4)

Now, in ∆ BCD :-

<B + <C + <D = 180° (angle sum property of ∆)
<ABC + <ACB + <ACD + <ADC = 180°

using (2) and (4) :-

<ACB + <ACB + <ACD + <ACD = 180°
= 2<ACB + 2<ACD = 180°
= 2 (<ACB + <ACD) = 180°
= <ACB + <ACD = 180°/2 = 90°
= <C = 90°

hope this helps you