cos α= -0,007275 α=? (α is in grad ) how is this problem solved ?
Let's start by reviewing what the trig functions mean. The sin(a) = b tells you that the ratio b is made up of taking some angle a and taking its opposite side divided by the hypotenuse of the resultant right triangle. This let's us find a ratio b given some angle a. However, we're going to need to use a slightly different method to find a given some ratio b.
The inverse trig functions, as mentioned above, are sort of like the opposite operation to regular trig functions. sin^-1, cos^-1, and tan^-1 are all inverse functions (they are also sometimes written as arcsin, arccos, and arctan - don't worry, they mean exactly the same thing). The inverse trig functions tell us that, given some ratio b, what the angle would have to be. So, if sin(a) = b, then arcsin(b) = a.
The answer posted above is correct, and I hope this clarifies how to solve the problem.