Question

I need step by step instruction on this precal/trig problem to get an answer :/ Please help? Click on attached

Answer 1

So we're in quadrant 3. Which one is that.
What is 2/5 in decimal and which angle has that as its cosine?

Answer 2

Q3 is the lower left. 2/5 in decimal form is 0.4?

Answer 3

angle?

Answer 4

Not sure :/

Answer 5

Hang on, but you should have a function like that on your calculator.

Answer 6

I found one online
http://www.rapidtables.com/calc/math/Arccos_Calculator.htm
66.4 degrees
Sounds about right

Answer 7

So the angle with cosine 0.4 is 66.4 degrees. If we sketch that in the first quadrant you'll see that an x value of 2 and a radius of 5 looks about right. OK?

Answer 8

Yes, sounds right.

Answer 9

Now what we need to do is to rotate that guy into the third quadrant. The angle will be 180 degrees plus 66.4. Notice that since x < 0, cosine is now negative, as given in the problem.

Answer 10

Oh, yea, I understand

Answer 11

A = 180 + 66.4 = 246.4
A/2 = 123.2
cos (A/2) = ?

Answer 12

Hmm... -0.547?

Answer 13

Yep. A/2 is in quadrant 2, so cosine is negative.

Answer 14

So how would the final result look like? I'm sorry, I usually have multiple choice to choose from

Answer 15

Usually for something like this you would show your work, I'd put the steps we went through and why, and diagrams and everything. But the answer is just this number that we calculated. How do you enter your answers??

Answer 16

Oh o.k, simple enough. Thank you so much for your help, I really appreciate it!

Answer 17

yw