#color(white)=(sqrt2+sqrt5)/(sqrt2-sqrt5)#
#=((sqrt2+sqrt5))/((sqrt2-sqrt5))color(red)(*((sqrt2+sqrt5))/((sqrt2+sqrt5)))#
#=((sqrt2+sqrt5)(sqrt2+sqrt5))/((sqrt2-sqrt5)(sqrt2+sqrt5))#
#=((sqrt2+sqrt5)(sqrt2+sqrt5))/(sqrt2^2+sqrt2sqrt5-sqrt2sqrt5-sqrt5^2)#
#=((sqrt2+sqrt5)(sqrt2+sqrt5))/(2color(red)cancelcolor(black)(+sqrt10-sqrt10)-5)#
#=((sqrt2+sqrt5)(sqrt2+sqrt5))/(2-5)#
#=((sqrt2+sqrt5)(sqrt2+sqrt5))/(-3)#
#=(sqrt2^2+sqrt2sqrt5+sqrt2sqrt5+sqrt5^2)/(-3)#
#=(2+sqrt10+sqrt10+5)/(-3)#
#=(2+2sqrt10+5)/(-3)#
#=(7+2sqrt10)/(-3)#
#=-(7+2sqrt10)/3#
This is the answer. You can verify using a calculator:
