Question

If the measure of each of the equal angles of an isosceles triangle is 55°, which of the following
represents the measure of the third angle?
(a) 100°
(b) 50°
(c) 80°
(d) 70°​

Answer 1

55 + 55 + x = 180

110 + x = 180

180 - 110 = 70

so D is the answer.

Answer 2

As we know

Iɴ Isᴏᴄᴇʟᴇs ᴛʀɪᴀɴɢʟᴇ ᴛᴡᴏ ᴀɴɢʟᴇs ᴀʀᴇ ᴇϙᴜᴀʟ.

Sᴏ, Lᴇᴛ ᴛʜᴇ ᴇϙᴜᴀʟ ᴀɴɢʟᴇ ʙᴇ x

Given:-

$x = 55^o$

To Find :-

Tʜɪʀᴅ ᴀɴɢʟᴇ $=> ? = y$

Solution :-

$x + x + y = 180^o$ [Angle sum property of triangle]

$55^o + 55^o + y = 180^o$

$110^o + y = 180^o$

$y = 180^o - 110^o$

$y = 70^o$

Tʜᴇʀᴇғᴏʀᴇ,Tʜɪʀᴅ ᴀɴɢʟᴇ ᴏғ ᴛʜɪs Isᴏsᴄᴇʟᴇs ᴛʀɪᴀɴɢʟᴇ ɪs $77^o$