S1=x2+y2+5Kx+2y+K=0
S2=x2+y2+Kx+2y+21=0
∴ Equation of common chord is S1−S2=0
⇒4Kx+23y+(K−21)=0....(1)
Give equation of common chord is 4x−5y−K=0....(2)
\because (1)&(2) are identical
∴44K=−523=−KK−21
Clearly, no value of K satisfy simultaneously.