Question

ABCD is a quadrilateral where AB=AD = 5, BC=CD = 7 and DAB = 80 degrees. Find the length of AC.

I've tried using law of cosines, but I got the wrong answer. I'm having trouble visualizing this, and I think I'm making invalid assumptions. Any help is greatly appreciated.

Answer 1

do you can drawing it ?

Answer 2

How did you get the 70 degrees? Thank you very much for your response, by the way.

Answer 3

you have wrote in the text of this exersice ,or not ?

Answer 4

Yes, I have wrote the complete text

Answer 5

so there you have wrote 70 degree ,or not ?

but on your drawing have wrote 80 degree ,why ?

Answer 6

I'm really sorry, it was supposed to be 80 degrees. I can't believe I missed it. Thank you for your patience

Answer 7

so than 80 is correct and not 70 ?

Answer 8

Yes, that's correct, sorry for the confusion.

Answer 9

lt AC = l_1 +l_2

us cos 40 = l_1 / 5 so l_1 = 5*cos 40 = 5*0,66 = 3,3

and cos 40 = l_2 / 7 so l_2 = 7*cos 40 = 7*0,66 = 4,62

so than AC = 3,3 +4,62 = 7,92

hope so much that is understandably

good luck

Answer 10

Thank you for your response, but I don't believe you can use cosine(or sine) because the angle bisector does not form a right triangle...unless I'm misunderstanding how you're dividing the quadrilateral.

Answer 11

The text says the answer is either 10, 9.07, 9.19 or 7.71. It's a review sheet for a class I'm starting next week.

Answer 12

so the right answer will be 7,71

Answer 13

this mean than was considered cos 40 = 0,6 and not 0,66

hope this will help you

Answer 14

This helps very much, I appreciate your help tremendously. I ended up finding 7.71, as you said, except I used 5*sin40+7*sin40; I'm guessing we "cut up" the quadrilateral differently. Thank you so much for your help!!!