Sin properties - Why is this undefined? Why is sin(-π/2)^(1/2) undefined? sin(-π/2) is -1, so I thought the the answer would be the same, -1^(1/2)=-1?  But my calculator and the answers sheet both say undefined...
Why do you think the principal square root of $-1$ is $-1$? That would suggest that $(-1)^2=(-1)\times(-1)=-1$ when clearly $(-1)\times(-1)=+1$. Instead, we have $(-1)^\frac12=i$ -- have you learned about imaginary numbers yet?
What everyone else is saying is -1^(1/2) is undefined, because anything ^(1/2) means it's the square root. (AKA x^(1/2) = sqrt(x)). (-pi/2) is negative so trying to get a square root of it doesn't work, and is therefore undefined.