Question

17. A triangular advertising board is 13 dm, 14 dm and 15 dm in length. Find the cost of painting it at 10 per dm?​

Answer 1

Question -

A triangular advertising board is 13dm,14dm and 15 dm in length. Find the cost of painting it at ₹10 per dm²

Solution -

Let,

a=13 dm

b=14 dm

c= 15 dm

We know that,

$s(semi \: perimeter) = \frac{a + b + c}{2}$

Now by putting the values of a,b and c we will get,

$s = \frac{13 + 14 + 15}{2}$

$s = \frac{42}{2}$

$s = 21$

Now by applying heron's formula we will get -

$Area \: of \: triangle = \sqrt{s(s - a)(s - b)(s - b)}$

$Area \: of \: triangle = \sqrt{21(21 - 13)(21 - 14)(21 - 15)}$

$Area \: of \: triangle = \sqrt{21 \times 8 \times 7 \times 6}$

$Area \: of \: triangle = \sqrt{7056}$

$Area \: of \: triangle = 84$

Therefore the area of a triangular advertising board is 84 dm²

Now,

Cost of painting per dm²= ₹10

Cost of painting 84 dm²= ₹(10×84)

=₹840

Therefore the cost of painting 84 dm² is ₹ 840

Answer 2

Answer:

answer is 84 dm*2 ₹840

this answer is help u