Question: I want to make a program that can calculate physics equation where the user enters different parameters: I know its simple like:

```
v=5
t=7
s=v*t
print(s)

```

its only calculating `s = v*t`; however, when I want the equation of `v` if show me an error. Hard coding `v = s/t` gives me the correct result:

```
s=5
t=7
v=s/t
print(v)

```

I want an equation that can solve with different user input; that is if user inputs the `v` and `t` , the equation will return `s = v*t` and if the user inputs `s` and `t` the equation will return `v = s/v`.

Answer: 
Assuming you're talking about the zero acceleration "svt" equations (or even the constant acceleration "suvat" ones, should you have more complex requirements), it's a simple matter of detecting what's unknown, and then filling in the gaps.

The following code provides a function that will do this along with some test code so you can see it in action:

```
# Returns a 3-tuple containing [displacement(s), velocity(v), time(t)],
#    based on the existence of at least two of those.
# If all three are given, the displacement is adjusted so that the
#    equation 's = vt' is correct.

def fillInSvt(s = None, v = None, t = None):
    # Count the unknowns, two or more means no unique solution.

    noneCount = sum(x is None for x in [s, v, t])
    if noneCount > 1: return [None, None, None]

    # Solve for single unknown (or adjust s if none).

    if noneCount == 0 or s is None: return [v*t, v, t]
    if v is None: return [s, s/t, t]
    return [s, v, s/v]

# Test code.

print(fillInSvt(99,4,6))         # Show case that adjusts s.

print(fillInSvt(None,4,6))       # Show cases that fill in unknown.
print(fillInSvt(24,None,6))
print(fillInSvt(24,4,None))

print(fillInSvt(24,None,None))   # Show "not enough info" cases.
print(fillInSvt(None,4,None))
print(fillInSvt(None,None,6))
print(fillInSvt(None,None,None))

```

The output shows that the tuple is filled in in all cases where there's a unique solution:

```
[24, 4, 6]
[24, 4, 6]
[24, 4.0, 6]
[24, 4, 6.0]
[None, None, None]
[None, None, None]
[None, None, None]
[None, None, None]

```
```
def h2(v,d,t):
    title_ar = 'السرعة'
    title_en = 'speed'
    if v=='':
        print("v= ","%.2f"% (d/t),"m/s")
    elif d=='':
        print("d= ","%.2f"% (v*t),"m")
    elif t=='':
        print("t= ","%.2f"% (d/v),"s")
    else:
        print("please write all data.")

h2('', 2,6)
h2(70,'',8)
h2(25,3,'')

```