due to the parallel nature of the 2 lines there is a symmetry effect for such shapes inscribed a circle. the upper and the lower triangle must be similar. and when applying a vertical line through the central crossing point, everything to the left is mirrored by everything on the right.

so, angle c must be equal to angle b.

c = 40°

and as the sum of all angles in a triangle is always 180°, d is then

d = 180 - 40 - 40 = 100°

the interior angle of the arc angle a is the supplementary angle of d (together they are 180°), because together with d they cover the full down side of the top-left to bottom-right line.

interior angle to a = 180 - 100 = 80°

due to the symmetry again, the arc angle opposite to a is the same as a.

as we know, the interior angle to a pair of opposing arc angles is the mean value of the 2 angles.

so, we have

(a + a)/2 = 80

2a/2 = 80

a = 80°

there might (and actually should) be some more direct approaches for "a" out of the other pieces of information, but that was the most straight one right out of my mind, and I don't spend time on finding additional shortcuts, when I have already a working approach.

8 0

2 years ago

Geometry math question no Guessing and Please show work

WITCHER [35]

Answer: Choice A) 15 feet

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x = length of fourth side in quadrilateral ABCD

Have a look at the attached image I've posted. I made a chart that lines up the side lengths from largest to smallest. Note how the first two items in the bottom row are blank. We don't know these values and we don't need to find out in order to find x.

Based on the last two columns of that table, we can form the proportion below, which is then used to isolate x.

30/12 = x/6

30*6 = 12*x ... cross multiply

180 = 12*x

12*x = 180

x = 180/12 ... divide both sides by 12

x = 15

5 0

3 years ago