# Homework Help: Proof of inverse trigonometric identities

1. Aug 14, 2011

### seboastien

1. The problem statement, all variables and given/known data

Show that arcsin(1/sqrt(5)) + arcsine(2/sqrt(5)) = Pi/2

2. Relevant equations

3. The attempt at a solution

Can someone please give me so much as a hint?

2. Aug 14, 2011

### ehild

Take the sine of the left-hand side and see if it is equal to sin(pi/2)

ehild

3. Aug 14, 2011

### dynamicsolo

Look at each term individually. Each is the arcsine of a ratio, so each term is an angle.

For the first term, if theta = arcsin(1/√5) , then sin(theta) = 1/√5 . Draw a right triangle with one angle being (theta) and having the side opposite (theta) equal to 1 and the hypotenuse equal to √5 . What is the side adjacent to (theta) equal to?

Now, is there an angle in that triangle having a sine of 2/√5 ? If so, it would be an angle which is the arcsine of (2/√5) . Call it (phi) . What do (theta) and (phi) add up to?

4. Aug 14, 2011

### PeterO

Draw a triangle and use pythagorus. [Just hints, not answers]