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Homework Help: Goemetry perimeter problem

  1. Jun 22, 2017 #1
    1. The problem statement, all variables and given/known data
    there is a circle with radius 9cm centred at o
    segment oa is 15cm
    ab, ca and pq are tangents to circle at points b,c and r respectively
    find perimeter of triangle apq

    2. Relevant equations

    3. The attempt at a solution
    i have solved the problem and got the right answer with two methods but i feel none of the methods is proper per say
    method 1:
    since the question is not imposing any restriction on the location of point r i assumed the perimeter is invariant with respect to r and hence let the segment pq fall on segment ca essentially the perimeter of two triangles is now just the two times the length of ac
    ac is 12 cm by pythagoras hence the perimeter of triangle is 24 cm
    a really crude method really dont think it is correct
    method 2:
    once with the assumption that the perimeter is invariant with respect to r
    i shifted r right up to the point where da intersects the circle
    then the triangle rpa is similar to triangle boa then rp is 9/2 and pa is 7.5 cm
    then perimeter is once again 15 + 9 = 24 cm
    however i feel my assumption is wrong and the question can be solved without the assumption so someone please help? thanks
  2. jcsd
  3. Jun 22, 2017 #2


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    How are the segments BP and PR related? The same with RQ and CQ?
  4. Jun 22, 2017 #3
    BP = BR and RQ = CQ
    and i also note that triangle PRO is similar to ORQ
    ok that is smart thanks
    perimeter = PA + PQ + AQ = BA - BP + CA - CQ + PQ = BA + CA- PQ + PQ = 24 thanks
  5. Jun 22, 2017 #4


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    Homework Helper

    Are they??
    It was simple, was not it? :smile:
  6. Jun 23, 2017 #5
    wait no they are not sorry my bad

    yup it was simple
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