
Al P. answered 10/06/20
Precalculus tutoring
sin-1(√2 / 2) = 45o ( = π/4 radians)
To see this, draw a right triangle with one leg along the x-axis, one leg parallel to the y-axis, and finally draw the hypotenuse from the origin to the end of the leg parallel to y-axis. Label the hypotenuse 2, and the leg parallel to the y-axis √2. Now the length of the leg along the x-axis is √ (22 - (√2)2 ) = √ (4 - 2) = √2 which means the triangle drawn has angles 45-90-45.

Al P.
Oh, yes, the answer from the other tutor is more complete. I was only considering quadrant 1, there is the symmetrical angle in quadrant 2 (180 degrees - 45 degrees = 135 degrees). And I only considered the principal angle (i.e. 0 <= angle < 360 degrees) which is typical for inverse trig functions. Of course, every 360 degree rotation repeats things for both of these angles, though providing just the principal angle is usually implied unless the problem explicitly asks for "all angles."10/06/20