SOLUTION: Please help me work out sec(sin-1(3/4)

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Question 245585: Please help me work out
sec(sin-1(3/4)

Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
This can be done using a calculator but you have to know how and even then you will only get a decimal approximation of the exact answer.

We can do this without calculators fortunately. sin-1(3/4) represents an angle whose sin is 3/4. Let's draw a picture of such an angle. (Note: the drawing is not to scale.)

A is the angle whose sin is 3/4. Note how the opposite side is 3 and the hypotenuse is 4. This makes the sin 3/4! To find the sec of A we need the adjacent side, x. To find x we can use the Pythogorean Theorem:
x%5E2+%2B+3%5E2+=+4%5E2
x%5E2+%2B+9+=+16
x%5E2+=+7
x+=+sqrt%287%29
Sec is hypotenuse over adjacent so
sec(sin-1(3/4) = 4%2Fsqrt%287%29
This is the exact answer. But normally we do not leave square roots in denominators so we will multiply the numerator and denominator by sqrt%287%29:
sec(sin-1(3/4) = %284%2Fsqrt%287%29%29%28sqrt%287%29%2Fsqrt%287%29%29
sec(sin-1(3/4) = 4sqrt%287%29%2F7
which is the exact answer with a rational denominator.