# Im I right??

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• May 31st 2013, 11:29 AM
kakashi
Im I right??
I solve these two equations and I got x=51.65degree but in my book x=128.35
so Iam confused
the equations are:
54.684=F Cos x...........(1)
69.313=F Sin x.............(2)
• May 31st 2013, 12:08 PM
HallsofIvy
Re: Im I right??
IF the question is as you stated it, "128.35" is impossible because if F is positive F cos x would be negative and if F is negative, F sin x would be negative.
• May 31st 2013, 12:24 PM
kakashi
Re: Im I right??
sorry
the first equation is negative
• May 31st 2013, 01:44 PM
HallsofIvy
Re: Im I right??
So your equations are F cos(x)= -54.684 and F sin(x)= 69.313?

Then clearly 51.65 degrees cannot be correct. I presume neglecting the negative was your error in doing the calculation and you see now that
128.35 degrees is correct? (Actually, I get 128.27 degrees.)
• Jun 1st 2013, 01:27 AM
kakashi
Re: Im I right??
why??
I got tan(x)=-1.264 and when you take the enverse of tan the answer will be x=-51.65
so can explain how did you solve it,please
• Jun 1st 2013, 01:53 AM
Prove It
Re: Im I right??
Surely you know that if sine is positive and cosine is negative then your angle is in the second quadrant.

The arctangent function is defined to only give angles in the fourth and first quadrants to make it a one to one function.