finding a value sin A=?   cos A = -(3/5) 90 degrees < A < 180 degrees  

Expert Answers

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Given that cos(A) = -3/5

We need to find sin(A) suchthat A is in the second quadrant.

First let us calculate the value of sin(A).

We know that sin^2 A + cos^2 A = 1

==> sin^2 A = 1- cos^2 A

==> sin^2 A = 1- (-3/5)^2

                     = 1- 9/25

                       = 16/25

==> sin(A) = +- 4/5

But since A is in the 2nd quadrant, then we know that the sine is positive.

==> sin(A) = 4/5

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