Question

Two sides of a triangle are 12cm and 5 cm and its perimeter is 30 cm then the third side will be​

Answer 1

$\bold{Given}\begin{cases}\sf \: Two \: sides \: of \: a \: triangle \: are \: \bold{12cm} \: and \: \bold{5cm}. \\ \\ \sf \: Perimeter \: of \: the \: triangle \: is \: \bold{30cm}. \end{cases}$

We've to find the third side of the triangle.

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As we know that : -

$\underline{\boxed{\sf\blue{\bigstar \: perimeter \: of \: a \: rectangle \: = sum \: of \: all \: sides}}}$

Here

First side of the triangle (a) = 12cm

Second side of the triangle (b) = 5cm

Perimeter of the triangle (P) = 30cm

Put the values : -

$\tt:\implies \: p \: = a + b + c \\ \\ \\ \tt:\implies \: 30 = 12 + 5 + c \\ \\ \\ \tt:\implies \: 30= 17 + c \\ \\ \\ \tt:\implies \: c = 30 - 17 \\ \\ \\ \tt:\implies \: c = \underline{\boxed{\sf\red{13cm}}}\bigstar \\ \\ \\ \\ \sf\therefore{\underline{Hence, \: the \: third \: side \: of \: the \: triangle \: \bold{13cm}.}}$

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Answer 2

$\underline{ \huge \bold \red{Answer}}$

Perimeter=1st side+second side+3rd side

Let 3rd side be x

30=12+5+x

30=17x

x=30-17

x=13

So, the third side will be 13 cm.