• double_quack@lemm.ee
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    3 days ago

    Sequence of lines to focus on to get to the answer

    making the BOLD ASSUMPTION that the angle of the arch is 90deg (the bottom right corner of your diagram), then the dashed lines will lead you to the value of the bold line.

    If the original assumption is correct, then the answer is 15.

      • mic_check_one_two@lemmy.dbzer0.com
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        3 days ago

        This is the worst way to go about doing it, because you should never assume a drawing is made to scale unless it is specifically marked as such. A protractor would be useless if the drawing isn’t to scale. Generally speaking, if a problem isn’t drawn to scale, it’s because all of the info you need to solve it is already present in the drawing. You don’t need to bust out the protractor to measure angles, because the angles can either be calculated from the available info, or aren’t needed in the first place.

  • TheSlad@sh.itjust.works
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    5 days ago

    24 and 7 make a pythagorean triple with 25 as the hypotenuse. If the problem uses one pythagorean triple, it probably uses another, so I assume x is 15, and the radius is 20.

  • juliebean@lemm.ee
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    6 days ago

    if we assume the bottom right corner is a right angle and is the center of the arc, then it is solvable in the manners that others here have already described. if either of those is not the case, and the image itself doesn’t state, then there is insufficient information to solve it.

  • Visstix@lemmy.world
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    6 days ago

    Well the drawing is wrong. I measured it with a ruler and it should be 9

  • xmunk@sh.itjust.works
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    6 days ago

    I assume you need to calculate the red triangle’s hypotenuse but it seems like there are too many degrees of freedom to lock down any of the other sides or angles of the triangle including X unless I’m missing some hack involving chords and reflected angles.

  • renormalizer@feddit.org
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    6 days ago

    x = 15

    Denote the origin of the circle O and the points A, B, C clockwise starting from the left. From the isosceles triangle OAB we get 2 r sin(alpha/2) = 24, where alpha is the angle between OA and OB.

    Construct the line orthogonal to OB that goes through C. The length of the line, h, between C and the intersection is h = 7 sin(beta) = x sin(90 - alpha). Denote the lengths of the parts of OB a and b, where a is connected to B. We have a + b = r

    Use Thales circle theorem to find that the triangle ABA’ completes the red shape, with A’ on the circle opposite to A. That means that the angle between A’A and A’B is alpha/2, but A’OB is also an isosceles triangle. So the angle on the other side, beta, has to be the same. Thus, beta = alpha/2.

    Now, put everything together: a = 7 cos (alpha/2), b = h cot(90 - alpha) = 7 sin(alpha/2) tan(alpha), r = 12 / sin(alpha/2).

    a + b = r <=> cos(alpha/2) sin(alpha/2) + sin^2(alpha/2) tan(alpha) = 12 / 7

    1/2 sin(alpha) + 1/2(1 - cos(alpha)) tan(alpha) = 12/7 <=> tan(alpha) = 24/7

    From the identity for h we know that x = 7 sin(alpha/2) / cos(alpha). Insert alpha = arctan(24/7)

  • ramble81@lemm.ee
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    6 days ago

    The two red lines are at a right angle, you can connect them and solve for the hypotenuse using the normal a^2 + b^2.

    At this point you now have a second triangle that contains the X you want. Also, since the outer shape is a quarter-circle (assumed) you know that the corner in the bottom right is 90 degrees which makes the two side equal in length.

    Since it’s an equilateral triangle, and you know the hypotenuse, you can back it out with c^2 = 2a^2 and solve it that way.