If the lines `3x+by-1=0` and `ax-5y+2=0` are parallel, then find the relation between `a` and `b`.

Explanation

`3x+by-1=0`
Slope `m_(1)=-("Coefficient of " x)/("Coefficient of " y)=-(3)/(b)`
and `ax-5y+2=0`
slope `m_(2)=-("Coefficient of " x)/("Coefficient of " y)=-(a)/(-5)=(a)/(5)`
For parallel lines
`m_(1)=m_(2)`
`implies (-3)/(b)=(a)/(5)`
`implies ab=-15`
Which is required relation.