Thread: Finding trig functions with one known function

I have a review packet that will be almost exactly like a test I will have and I'm stuck on some problems and here is one that is like the rest:

If sin0= -4/7 and cos0 > 0, find sec0

I'm mostly confused because of the negative sine since obviously you can't measure a line and get negative inches.

Can someone show me how they can get the answer for this so I will be able to do similar problems to this on the test?

Originally Posted by clay10

I have a review packet that will be almost exactly like a test I will have and I'm stuck on some problems and here is one that is like the rest:

If sin0= -4/7 and cos0 > 0, find sec0

I'm mostly confused because of the negative sine since obviously you can't measure a line and get negative inches.

Can someone show me how they can get the answer for this so I will be able to do similar problems to this on the test?

The sine of an angle is the ratio of the opposite leg of the triangle divided by the hypotenuse. If this ratio is negative, it means that the opposite leg points downward. However this can happen in quadrants III and IV, so you need to use the fact that the cosine of the angle (adjacent divided by hypotenuse)is positive to figure out which quadrant the angle is in.

Help?

sort of... on my paper the negative symbol for the sine doesn't belong to the 4 but I doubt that makes a difference... if you don't mind could you give me the answer, then I'll know exactly how to do these types of problems

Originally Posted by clay10

sort of... on my paper the negative symbol for the sine doesn't belong to the 4 but I doubt that makes a difference... if you don't mind could you give me the answer, then I'll know exactly how to do these types of problems

I'm sorry but I do mind. I will help you through the problem though. Cmon, you can do it!

You know that sine, cosine and the other trig ratios all come from right triangle ratios right? Draw your x and y axes, then think about which quadrant the angle is in. Like I said because sin(x)<0, then leg parallel to the y-axis must be facing down, making it negative. Thus it has to be in the quadrant III or IV (bottom left or bottom right).

Are you with me so far?

No... thanks for the help but I'd rather have a demonstration

Originally Posted by clay10

No... thanks for the help but I'd rather have a demonstration

We don't give out answers here, I'm sorry. If you are unwilling to put any work into the learning process then you have found the wrong place.

If you change your mind, PM me and I'll reopen the thread.