The line xa−yb=1 cuts the x-axis at P. The equation of the line through P perpendicular to the given line, is
x+y=ab
x+y=a+b
ax+by=a2
bx+ay=b2
The line xa−yb=1 cuts x-axis at P(a,0). The equation of the line through P(a,0) and perpendicular to xa-yb=1, is
y−0=−ab(x−a)⇒ax+by=a2