Question

The semi perimeter of a triangle is 20 cm. If two of the sides are 10 cm and 15 cm, find the length of the third side.​

Answer 1

Answer:

15 cm

Step-by-step explanation:

Let a, b and c be the 3 sides of the triangle.

Given:

semi-perimeter = 20 cm, a = 10cm, b = 15cm

Perimeter = 2*semi-perimeter  =  2*20

Perimeter = 40cm

We know that perimeter is the sum of all the sides.

a+b+c = 40

10+15+c = 40

c = 40-25 = 15

Thus, the length of the third side is 15cm.

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Answer 2

Answer:

third side = 15cm

Step-by-step explanation:

perimeter = semi perimeter * 2

perimeter = 20 * 2 = 40

perimeter = sum of all three sides of a triangle

40 = 10 + 15 + x

x = 40 - 10 -15

x = 40 - 25

x = 15