Given angle A=angle C.
The objective is to find the perimeter of the isosceles triangle ABC.
First let's find the value of x.
An isosceles triangle contains two equal sides. Here angle A and angle C are equal. So the sides AB and AC are equal.
[tex]\begin{gathered} AB=BC \\ 5x-1=3x+11 \\ 5x-3x=11+1 \\ 2x=12 \\ x=\frac{12}{2} \\ x=6 \end{gathered}[/tex]
Now, find the perimeter of the triangle by adding all the sides of the triangle.
[tex]P=5x-1+3x+11+x+19[/tex]
Substittue the value of x =6.
[tex]\begin{gathered} P=5(6)-1+3(6)+11+6+19 \\ P=30-1+18+11+6+19 \\ P=83 \end{gathered}[/tex]
Hence, the perimeter of the triangle is 83.
[tex]\begin{gathered} \text{Let's check the whether the obtained x value if correct.} \\ AB=BC \\ 5x-1=3x+11 \\ 5(6)-1=3(6)+11 \\ 30-1=18+11 \\ 29=29 \end{gathered}[/tex]
Thus the sides of isoscles triangles are equal. Hence the value of x is correct.