Find the sides of an isosceles triangle if one of them is 30 cm less than the perimeter, and the other is 40 cm.

Let a cm – the length of the equal sides of an isosceles triangle, and b cm – the length of its base.

The perimeter will be calculated by the expression 2a + b cm.

Let’s compose and solve a system of equations.

2a + b – 30 = a;
2a + b – 40 = b.

2a = 40;
a = 20 cm.

b = 30 – a = 30 – 20 = 10 cm.

Answer: the sides of the triangle are 20 cm and 10 cm.