Question

If x=1/7+4 x square root of 3 and y= 1/7-4 x square root of 3, find the value of x 3 + y 3

Answer 1

Do not use x as a symbol of multiplication, one may get confused it with variable x. instead use *.
However your soultion is
x^3+y^3= (x+y)^3-3xy(x+y)
=(14)^3-3*1*14=2702