Question

two side of triangle are 12cm and 9cm and the semi perimeter is 19 then find the third side​

Answer 1

Semiperimeter = 1/2*perimeter(sum of all sides)
Therefore, 19=1/2* perimeter
Therefore, your perimeter is 38cm
Let the third side be x
12+9+ x =38
21+ x=38
Therefore your answer of the third side is 17 cm

Answer 2

☆Given :

• 1 side = 12 cm

• 2 side = 9cm

• half perimeter = 19 cm

$\rightarrow$ full perimeter = 19 + 19

= 38 cm

$\large \boxed{perimeter = s + s + s}$

• Let 3rd side be = x

$\rightarrow$ 38cm = 12 + 9 + x

$\rightarrow$ 38 cm = 21 cm + x

$\implies \: 38 - 21 = x$

$\implies \: 17 = x$

$\therefore$ 3rd side = 17 cm