x^2+1/x^2=(x+1/x)^2-2=3^2-2=7x^4+1/x^4=(x^2+1/x^2)-2=7^2-2=47
x+1/x=-3,(x+1/x)^2=x^2+2+1/x^2=9∴x^2+1/x^2=7,(x^2+1/x^2)^2=x^4+2+1/x^4=49,∴x^4+1/x^4=47