If xy+yx=−1, where x,y≠0 then the value of (x3−y3) is (a) 1
(b)−1
(c) 0
(d) 12
ANSWER: (c) 0 xy+yx=−1
⇒x2+y2xy=−1 ⇒ x2+y2=−xy ⇒ x2+y2+xy=0
(x3−y3)=(x+y) (x2+y2+xy)=0
Hence, (x3−y3)=0