Problem Solving

the sin of angle B is 28/35. the angle measure is therefore sin -1( 28/35 ); angle B is approx 53.1 degree

My question is how do we get the value of angle B as 53.1 degree ?

pls explain in detail

You will never be asked to find the exact values of sin -1( 28/35 ).

What you can be asked is : Sin B = 28/35 then what is cos B or tan B. This seems logical.

Anyway, there is no way to find the exact value of 53.1 degree, unless you are provided with a trigonometric chart or a calculator.


Thanks !!

As avik.ch said
GMAT would never ask a question where you would need to find the value of sine inverse


But if you were given options such as these:
A. 17.4
B. 34.8
C. 43.9
D. 53.1
E. 69.3


Heres how I would have done it:
Sin(0) = 0
As we increase the angle, sin also increases until sin(90) = 1


sin(x) = 28/35 = 4/5 = 0.8
sin(45) = 1/sqrt(2) = 0.7
sin(45) < sin(x)
45<x
Option A, B, and C are eliminated

sin(60) = sqrt(3)/2 = 0.86
sin(60) > sin(x)
60 > x
Option E also eliminated

Option D is correct



If two options were given between 45 and 60, we cannot find the ans and neither does GMAT expect us to.

Trigonometry is not tested on the GMAT. Any problem that discusses the sine, cosine or tangent of an angle -- or requires knowledge of these properties -- is not a legitimate GMAT question.

The law has already been stated by Mitch sir.

That is the reason why OG never uses any trigonometry to explain any problems.