Hello from MrBillDoesMath!
Answer:
23
Discussion:
In ΔABC side AC is 11, but as the triangle is isosceles the other leg also has length 11. Let the third, unknown side, be called x. Then
11 + 11 + x = Perimeter = 45.
11 + 11 + x = 45 => as 11 + 11 = 22
22 + x = 45 => subtract 22 from both sides
x = 45 -22 = 23
Thank you,
MrB
