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Re: What is the measure of the radius of the circle inscribed in a triangl [#permalink]

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15 Jun 2011, 22:12

soaringAlone wrote:

What is the measure of the radius of the circle inscribed in a triangle whose sides measure 8, 15 and 17 units?

A. 8.5 units

B. 6 units

C. 3 units

D. 5 units

E. 12 units

Note: From the options provided, its easy to pick the answer right aways but I would want to know the computation steps.

Sides are 8, 15 and 17...thus it is right angle triangle Since 17^2 = 8^2 + 15^2 therefore, area = 1/2 * 15 * 8 = 60

We have to find in-radius Therefore, area of triangle = S*r ....where S=semi-perimeter and r= in-radius Now S=semi-perimeter = 17+15+8 /2 = 20 Thus , 60 =20*r and hence r=in-radius= 3

Re: What is the measure of the radius of the circle inscribed in a triangl [#permalink]

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18 Jun 2011, 19:40

vyassa,

dint get it below part .Is thia some standard formulas for semi perimeter .

We have to find in-radius Therefore, area of triangle = S*r ....where S=semi-perimeter and r= in-radius Now S=semi-perimeter = 17+15+8 /2 = 20 Thus , 60 =20*r and hence r=in-radius= 3
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Re: What is the measure of the radius of the circle inscribed in a triangl [#permalink]

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18 Jun 2011, 21:50

2

This post received KUDOS

well there is a formula for area of the triangle and that is S*r.... In the given formula S is the semiperimeter i.e. half of the perimeter of the triangle. e.g. if a,b, and c are the sides of the triangle then perimeter will be a+b+c and semiperimeter will be (a+b+c)/2

Now, inradius is the radius of the circle that is inscribed in a triangle. In the given figure billow OP is an inradius.

Now, what all we know is three sides of the triangle, thus perimeter and area of triangle i.e. 60 Thus the easiest and fastest way is to apply the formula S*r = area of triangle therefore, 20*r = 60 ...hence r = 3

Since r is the inradius i.e. radius of the inscribed circle, we have found out the answer.

Re: What is the measure of the radius of the circle inscribed in a triangl [#permalink]

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19 Aug 2015, 00:49

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