Question

12. The perimeter of an isosceles triangle is 18 cm. If one of the equal sides is : 5
cm long,
find the measure of the third side.​

Answer 1

Answer:

another side is 8

Step-by-step explanation:

one equal side is 5

so twos sides are 5 and 5

Therefore,

5+5+x = 18 (since the perimeter is 18)

10+x =18

X. =8

Answer 2

Answer :-

• The measure of the third side is 8 cm.

To find :-

• The measure of the third side.

Step-by-step explanation :-

We know that :-

• A triangle in which two of the sides are equal is called an isosceles triangle.

It has been given that :-

• One of the equal sides is 5 cm long.

Therefore,

• The other equal side is 5 cm long too.

Now,

• Let the third side be "x".

It has been given that :-

• The perimeter of the triangle is 18 cm.

We know that :-

$\underline{\boxed{\sf Perimeter \: of \: a \: triangle = Sum\: of \:all \:sides}}$

Which means that :-

• The sum of 5 cm, 5 cm and x is 18 cm.

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Therefore,

$\longmapsto\rm x + 5 + 5 = 18$

Adding 5 and 5,

$\longmapsto\rm x + 10 = 18$

Transposing 10 from LHS to RHS, changing it's sign,

$\longmapsto\rm x = 18 - 10$

Subtracting 10 from 18,

$\longmapsto\overline{\boxed{\rm x = 8 \: cm}}$

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• Hence, the third side is 8 cm long.