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Mathematics 82 Online
OpenStudy (anonymous):

Please help! Give the Quadrant the angle terminates. angle A in Quadrant II, tanA=-12/5 angle B in Quadrant III, sinB=-3/5 cos ( A + B) = a. 56/65 b. -16/65 c. -56/65 d. 16/65

OpenStudy (anonymous):

Well you're going to have to make two triangles here. Solve for missing sides. Label one triangle A and the other Triangle B. Next find the identity for cos(A+B) because that equals something in terms of cos and sine if i'm not mistaken. But i'll be in terms of both angles.. But because of your work from the first step you'll be able to replace them with what you know from the triangles. :D Does that make sense?

OpenStudy (anonymous):

the answer is b

OpenStudy (anonymous):

Yes, that makes sense. I will start on the triangles. @hamish93 would you mind showing me how you got to that conclusion? I want to learn how to do it :)

OpenStudy (anonymous):

He may or maynot be right. We'll get to the correct answer doing it this way. :D

OpenStudy (anonymous):

I'm sorry, I have to leave my computer and log off for urgent reasons. :( Thank you for your help! I will take what you've taught me!

OpenStudy (anonymous):

hope everything is okay. Good luck.

OpenStudy (anonymous):

i did it the same why i showed you on the other question, i found what A and B equal and then put them into the correct trig equation

OpenStudy (anonymous):

@agentc0re could you test your way and see if my way works

OpenStudy (anonymous):

@hamish93 tested, msg sent. you should test it out. :D i know it works. hahaha.

OpenStudy (campbell_st):

learn to draw a diagram looking at angle A |dw:1343800944174:dw| find x using prthagoras and then you can get an exact value for sin(A) and cos(A) now for angle B |dw:1343801093862:dw| Again find y using pythagoras and again you will be able to get an exact value for cos(B) then use the expansion and substitute cos(A + B) cos(A) cos(B) - sin(A) sin(B)

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