+130477 If x is an obtuse angle whose sine = !/2, then x must lie in the second quadrant. This angle would be the same as a 30° reference angle in the first quadrant, i.e., 150 degrees. And cos(x) would have the same value as a 30 degree angle in the first quadrant, (√3)/2. except that it would be negative in the second quad.
+33658 Here are two pictures that might help. The first should enable you to get the magnitude of the exact value, and the second should enable you to get the sign right (remember that an obtuse angle is between 90 and 180).
+130477 If x is an obtuse angle whose sine = !/2, then x must lie in the second quadrant. This angle would be the same as a 30° reference angle in the first quadrant, i.e., 150 degrees. And cos(x) would have the same value as a 30 degree angle in the first quadrant, (√3)/2. except that it would be negative in the second quad.
