Question

find the area of triangle two side of which are 18 cm and 10 cm and the perimeter is 42cm

Answer 1

perimeter of a triangle = sum of all sides
42 = 18 + 10 + x
42 = 28 + x
42 - 28 = x
X = 14 cm

now we have the all the sides of the triangle,

Now apply Heron's formula to find the area

the formula is, Area of the given triangle=
$\sqrt{s(s - a)(s - b)(s - c)}$
s=
$\frac{a + b + c}{2}$
here, a, b and c are the lengths of the three sides of the triangle

Apply this and you will find the answer yourself