So (3a+b)(3a-b)=- 13.

So 3a-b=- 1.

Simultaneous solution: a=2, b=7.

Because this triangle is an isosceles triangle.

According to the conditions of triangle:

The three sides of this triangle are 2, 7 and 7 respectively.

So the perimeter of the triangle is 2+7+7= 16.