If a straight line knows the intersection (1, 0), it does not necessarily have a slope.

When the straight line is x= 1, although the straight line passes through the point (1, 0), the slope does not exist.

If it is assumed that the straight line is x=my+ 1, this situation can be included when m=0.

Pay attention to the conditions of the topic. If the slope must exist, it can be assumed that y = kx+b.

If you assume y=kx+b from the beginning, you will miss the possibility that the slope does not exist.