∵Re(u)+Im(u)=1 ⇒2x2+2y2−2Ky+y−K−2xy+2Kx+2xy+x =x2+y2+K2−2Ky Since, the curve intersect at y -axis ∴x=0 ⇒y2+y−K(K+1)=0 Let y1 and y2 are roots of equations if x=0 ∵y1+y2=−1 y1y2=−(K2+K) ∴(y1−y2)2=(1+4K2+4K) Given PQ=5⇒|y1−y2|=5 ⇒4K2+4K−24=0⇒K=2 or -3 as K>0,∴K=2