Given: (x+√1+x2)(y+√1++y2)=1 Concept used: A2−B2=(A+B)(A−B) (A+B)2=A2+B2+2AB (A−B)2=A2+B2−2AB Shortcut Trick Given that (x+√1+x2)(y+√1+y2)=1 Put x=0 and y=0 (Real number) ⇒(0+√1+02)(0+√1+02)=1 ⇒1×1=1 satisfied Hence, value (x+y)2 at x=0 and y=0 ⇒(0+0)2=0 ∴(x+y)2=0