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  • Isosceles Triangle 80-80-20

     Vivek updated 1 month, 1 week ago 2 Members · 6 Posts
  • Puzzle Prime

    Administrator
    October 22, 2020 at 7:52 am

    You are given an isosceles triangle ABC, ∠CAB = ∠ABC = 80°. Point D belongs to the side BC, so that AB = CD. Find the measure of angle DAB.

  • Vivek

    Member
    October 22, 2020 at 2:14 pm

    70 degrees. Using sine and cosine law of triangles, and standard trigonometric identities.

    • Puzzle Prime

      Administrator
      October 22, 2020 at 2:40 pm

      Yeah, trigonometry works well for this problem. Try to find the “pretty” solution now though:)

    • Vivek

      Member
      October 23, 2020 at 8:20 pm

      Got it!

    • Puzzle Prime

      Administrator
      October 23, 2020 at 8:26 pm

      Wow, I have never seen this solution before, good job! There are (at least) 2 other solutions involving equilateral triangles:)

    • Vivek

      Member
      October 23, 2020 at 8:40 pm

      Before your “pretty solution -clue”, I got that through lots of equations , changing 1/2 to sin 30 and the like. haha..This is cool! 🙂

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