Find the length of the third side of the triangle if its perimeter is 12 cm and the length is 3 cm and 4 cm.

To find out the perimeter, all sides must be folded. Then we fold the sides that we know
1) 3 + 4 = 7 (cm) – 2 sides together
Now get to know the side we don’t know
It is necessary to subtract the sum of the two sides from the perimeter
2) 12-7 = 5 (cm) – the third side of the triangle
Expression: 12- (3 + 4) = 5 (cm)
Answer: the third side of the triangle is 5 cm