[Tutor] Expecting a float but get an int

[Phil]

Help please.

This function returns "a" as .7 and "b" as 0 instead of .7. I'm sure the 
reason is obvious but I cannot see what it is.

def slope_intercept(x1, x2, y1, y2):
     a = (y2 - y1) / (x2 - x1) # a = .7 which is correct
     #a = .7

     b = (y1 - (a * x1) # b = 0 where it should be .7
     return a, b

slope, intercept = slope_intercept(9, 0, 7, 0)
print("slope :", slope, "intercept :", intercept)

This is what I've tried:

     a = float((y2 - y1) / (x2 - x1))

     b = float((y1 - (a * x1))

In the function:

x1 = float(x1)

the same for x2, y1, y2

The debugger show "a" and "b" to be floats.

The only way that I can have "b" show the correct answer is if I 
specifically make a = .7.

What have I overlooked?

-- 
Regards,
Phil