Radicals equations-negative square root and two radicals

[Coco12]

Is the answer to sqrt -81y^3 : y sqrt-81y? or is there no real solutions?

Also for this radical equation:
sqrt 2n-5 - sqrt 3n+4=2
I worked it out and can't seem to get an answer. Is there no real solutions?

 

[mfb]

if y<0, then $\sqrt{-81y^3}=|y|\sqrt{-81y}$, otherwise the square root is not defined in the real numbers.

Your equation has no real solutions. You can check this with WolframAlpha, for example.

 

[Coco12]

thank you so much, that WolframAlpha thing is very useful!

 

[dextercioby]

That $\sqrt{-81 y}$ can be further simplified by noting that 9² = 81 and -y = |y| , for y smaller or equal to 0.