Exercise 59 Page 452

In the given figure, we see that the sides of the triangle are congruent.

We know that a triangle with three congruent sides is equilateral. Therefore, the side lengths are equal. 7x = 11x-8 = x+12 Let's solve this equation for x using the first equality.

Now, we are ready to find the measures of the unknown sides by substituting the value of x. Remember that the triangle is equilateral.