I have assumed root(7)(265)7√265 was meant to be root(7)(256)7√256
256=2^8=2^7 * 2256=28=27⋅2
color(blue)(root(7)(256))=root(7)(2^7 * 2) = root(7)(2^7) * root(7)(2)color(blue)(=2root(7)2)7√256=7√27⋅2=7√27⋅7√2=27√2
-6root(7)2+2color(blue)(root(7)(256)−67√2+27√256
color(white)("XXX")=-6root(7)(2)+2*color(blue)(2root(7)(2))XXX=−67√2+2⋅27√2
color(white)("XXX")=-6root(7)(2)+4root(7)(2)XXX=−67√2+47√2
color(white)("XXX")=-2root(7)(2)XXX=−27√2