If cos A = .5417 and A is an angle between 0 and 90, find A. Round to the nearest tenth of a degree.
A. 57.2
B. 32.3
C. 16.9
D. 73.1

Question

If cos A = .5417 and A is an angle between 0 and 90, find A.  Round to the nearest tenth of a degree.
	A.	57.2
	B.	32.3
	C.	16.9
	D.	73.1

i<3mybaby · Answer

@Johnbc 
@dan815

anonymous · Answer

@mathmale

anonymous · Answer

What is the "opposite" of Cosine? So that we may apply it to both sides and eliminate the Cosine from the left and have "A" by itself

i<3mybaby · Answer

I was typing random numbers in my calc and some how got a.

anonymous · Answer

Well what do you say your answer for A is?

i<3mybaby · Answer

57.2

i<3mybaby · Answer

is that correct?

anonymous · Answer

We can verify by attempting the problem.
For the Cosine function, if we want to eliminate it from the left leaving only A we have to use its inverse $$Cos^{-1}$$
Applying this into our equation
$$Cos(A)= 0.5417$$
Cosine Inverse of both sides gets us
$$A = Cos^{-1}(0.5417) = 57.2 $$

So you are correct! and I hope that helps so that you understand how it is done

jim_thompson5910 · Answer

A is correct because

cos(A) = 0.5417
cos(57.2) = 0.5417
0.5417 = 0.5417

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Alternatively, you can isolate A using the arccosine function

cos(A) = 0.5417
arccos(cos(A)) = arccos(0.5417)
A = arccos(0.5417)
A = 57.2005596
A = 57.2