I have no idea how to prove these. Any solutions would be greatly appreciated.

1)

tan(x+y+z) = (tanx + tany +tanz - tanxtanytanz)/(1- tanxtany- tanxtanz-tanytanz)

2)

sin(pi/2 +x)cos(pi-x)cot(3pi/2+x)=sin(pi/2-x)sin(3pi/2-x)cot(pi/2+x)

3) csc^2(pi/2-x)=1+sin^2xcsc^2(pi/2-x)

Thanks in advance.