Wolfram|Alpha: Calculate an expression for $x^2y=-2$

Question

I would like to calculate the expression $(xy)^8*x^8$ knowing that $x^2y=-2$.
What should I write in Wolfram Alpha to get the expected result?

Kind regards,
Alexis.

Answer 1

Knowing that $$y=-\frac{2}{x^2}$$ you will get

$$\left(x\left(-\frac{2}{x^2}\right)\right)^8x^8=…$$ For your further work: The result is $$256$$ In WA you can use the replace Operator: $$(xy)^8x^8/.y->-2/x^2$$