# Geometry

#### Sana

##### New member
Hi all I need help in finding quadrilateral side and angles? Needs to divides two triangles.

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#### Otis

##### Elite Member
… [Need] to [divide the quadrilateral into] two triangles.
Hi Sana. Here's a hint: Draw a line from A to C. That's one way to begin.

Hopefully, you've already learned how to use the Law of Cosines and Law of Sines. (If not, then please tell us what class you're taking and what you've been studying recently.)

For triangle ACD, you've been given two sides and the angle between them. Use the Law of Cosines, to find side AC.

Side AC is opposite the 65º angle, so you can use the Law of Sines next to find angle ACD.

Once you know angle ACD, you can calculate angle CAD. (Let us know, if you're not sure how.)

After the steps above, there are two more steps to find side BC. Can you see what they are?

If you'd like more help with this exercise, please post your work so far or ask specific questions.

#### Sana

##### New member
Am I doing it right?

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#### Dr.Peterson

##### Elite Member
Am I doing it right?
No, you used the wrong angle. Read Otis's steps carefully.

#### Otis

##### Elite Member
Am I doing it right? …
Hi Sana. Were you able to continue, after reading Dr. Peterson's reply?

We use Law of Cosines when we know two sides and the angle between them.

Two sides in the diagram are 6 and 15, and the angle between them is 65º. In your work, you'd mistakenly written 140º.

Feel free to let us know, if you need any more help with this exercise.