The perimeter of the triangle is 20 in. Its two sides are equal and each of them is 1 dm larger than the third. Find the sides of the triangle.

take the unknown side as x
then equal sides (each) will be equal to x + 1dm
the perimeter is found by the formula: P = a + b + c
imagine that a = b = (x + 1); c = x
Let’s make the equation: 20 = (x + 1) + (x + 1) +1
20 = 3x + 2
20-2 = 3x
18 = 3x \: 3
6 = x
a = b = (6 + 1) = 7 (dm)
Answer: a = 7dm b = 7dm c = 6