if x=1+under root 2+under root 3 prove that x power 4-4 x cubed-4x squared+16x-8=0
How about some actual math notation?
is it
x=1+√2+√3
and
x^4-4x^3-4x^2+16x-8 = 0?
I don't see any useful tricks here. Just start expanding the powers.
x^4 = 80 + 48√2 + 40√3 + 32√6
Expand the others and then things will cancel out.