If then the value of is

If a-b=10 and ab=-21, then what is the value of a³-b³?

If , and y=2x, find x. 

If a²=b+c, b²=c+a  and c²=a+b then the  value of is

If bc+ab+ca=abc, then the value of is

x-y=2, xy=24, then the value of (x²+y²) is:

If then find the value of :

and then what is  the value of ?