How to find $x^4+y^4+z^4$ from equation? Please help me.
There are equations: $x+y+z=3, x^2+y^2+z^2=5$ and $x^3+y^3+z^3=7$. The question:
what is the result of $x^4+y^4+z^4$?
Ive tried to merge the equation and result in desperado. :(
Please explain with simple math as I'm only a junior high school student. Thx a lot

solution 2: since 
$$x^4+y^4+z^4=(x^2+y^2+z^2)^2-2x^2y^2-2y^2z^2-2x^2z^2$$
and
$$(xy+yz+xz)^2=x^2y^2+x^2z^2+y^2z^2+2xyz(x+y+z)$$
since
$$xy+yz+xz=2,xyz=-\dfrac{2}{3}$$
so $$x^2y^2+y^2z^2+x^2z^2=8$$
so
$$x^4+y^4+z^4=5^2-2\cdot 8=9$$
