Question

Two sides of a triangle are 5 cm and 4 cm. The perimeter of the triangle is 12 cm. The length of the third side is
21 cm
9 cm
3 cm

Answer 1

Answer:

3cm

Step-by-step explanation:

Given,

• Two sides of the ∆ are 5cm and 4cm
• Perimeter = 12cm

To find,

• The third angle

Options Given,

• 21cm
• 9cm
• 3cm

$\underline{\fbox{\fbox{\rm{Finding \: 3rd \: side:}}}}$

The perimeter of a triangle = 1st side + 2nd side + 3rd side

⇒12cm = 5cm + 4cm + 3rd side

⇒12cm = 9cm + 3rd side

⇒12cm - 9cm = 3rd side [Transposition]

⇒3cm = 3rd side

.°. The length of 3rd side is 3cm.

Hence, The last option 3cm is the right answer.

Answer 2

Given :-

Two sides of triangle are 5 and 4 cm

Perimeter = 13 cm

To Find :-

3rd  side

Solution :-

We know that perimeter is the sum of all sides

$\sf Perimeter = a + b + c$

$\sf 12 = 5 + 4 + c$

$\sf 12 = 9 + c$

$\sf 12 - 9 = c$

$\sf 3 = c$

Therefore,

Correct option c

Know More :

Area of triangle = ½ × b × h

Area of square = side²

Area of trapezium = ½(a + b)h