In triangle ABC, AB = AC, and angle A is equal to 36 degrees. Point D is on AC so that BD bisects angle ABC.

(a) Prove that BC = BD = AD.

(b) Let x = BC and let y = CD. Using similar triangles BCD and ABC, write an equation involving x and y.

(c) Let r = y/x. Write the equation from part (b) in terms of r, and find r.

(d) Find cos 36 degrees and cos 72 degrees using Parts a-c. (Do not use your calculator!)

Thank you so much! Pls include steps :)

Noori Oct 8, 2020

#1**0 **

You can prove that triangle ABC is a 30-60-90 triangle, with angle A = 30, angle B = 90, and angle C = 60. Then D is the midpoint of AC, so AD = CD = BD. The rest of the parts are easy.

Guest Oct 8, 2020

#4**+3 **

Enjoying week 24 of Int to Geo?

These have been solved here:

http://www.mathisfunforum.com/viewtopic.php?pid=413642

And also, don't try to get people to do the proof for you. You will be in a lot of trouble with the proof part if you are caught.

Nacirema Oct 8, 2020