The perimeter of an isosceles triangle is 21 cm. The length of each equal side is triple the length of the base. Find the side lengths of the triangle.

Let the length of the base of this isosceles triangle be = x

One of its equal sides = 3x

Another one of its equal sides = 3x

Their perimeter = x + 3x + 3x = 21 cm

To find the value of each side let us first solve this equation .

= x + 3x + 3x = 21 cm

= 7x = 21 cm

= x = 21 ÷ 7 ( transposing ×7 from LHS to RHS changes ×7 to ÷7 )

= x = 3

Then length of base = 3 cm

Length of one equal side = 3 × 3 = 9 cm

Length of another equal side = 3 × 3 = 9 cm

Therefore , the the three sides of this triangle = 3 cm , 9 cm and 9cm .

the correct answer would be the third option