color(white)=(sqrt2+sqrt5)/(sqrt2-sqrt5)=√2+√5√2−√5
=((sqrt2+sqrt5))/((sqrt2-sqrt5))color(red)(*((sqrt2+sqrt5))/((sqrt2+sqrt5)))=(√2+√5)(√2−√5)⋅(√2+√5)(√2+√5)
=((sqrt2+sqrt5)(sqrt2+sqrt5))/((sqrt2-sqrt5)(sqrt2+sqrt5))=(√2+√5)(√2+√5)(√2−√5)(√2+√5)
=((sqrt2+sqrt5)(sqrt2+sqrt5))/(sqrt2^2+sqrt2sqrt5-sqrt2sqrt5-sqrt5^2)=(√2+√5)(√2+√5)√22+√2√5−√2√5−√52
=((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:
