Would you define 2 equations with same gradient, x and y intercepts one which has infinite solutions?
Yes (as in they are the same so they intersect over their entire length).
Not sure if you've done much integration and stuff yet but the derivative is the gradient but you can think about it this way.
If
 = m(x) )
where m(x) is the gradient and
 = m(x) )
- given that the derivative gives the gradient.
Then
 = M(x) + c)
where M(x) is an antiderivative of m(x) and
 = M(x) + d)
where d is a constant.
Now if they both pass through a single point (so even if you only know that they pass through the same y-intercept)...Let's call this point (a,b)
 = b = M(a) + c)
 )
 = b = M(a) + d)
 )
Hence
 = M(x) - M(a) + b)
and
 = M(x) - M(a) + b)
So f(x) and g(x) are equal.
So any two equations with same gradient over all x which coincide at any one point are equal and intersect at every point