First of all, I'm going to assume that we have a concave down parabola, because the stream of water is subjected to gravity.
If we need the vertex to be at 
, the equation will contain a 
term.
If we start with 
we have a parabola, concave down, with vertex at and a maximum of 0.
So, if we add 7, we will translate the function vertically up 7 units, so that the new maximum will be 
We have
Now we only have to fix the fact that this parabola doesn't land at 
, because our parabola is too "narrow". We can work on that by multiplying the squared parenthesis by a certain coefficient: we want
such that:
Plugging these values gets us
As you can see in the attached figure, the parabola we get satisfies all the requests.
No reason, or no evidence to support your claim/proof
The external angle is suplementary to the internal angle close to it. We also know that the sum of all the internal angles of the triangle are equal to 180 degrees, this means that the angle "a" is suplementary to the sum of the angles "b" and "c". Through this logic, we can conclude that since:
Then we can conclude that:
Therefore the statement is true, the exterior angle is equal to the sum of its remote interior angles.
Let's use an example:
On this example, the external angle is 120 degrees, therefore the sum of the remote interior angles must also be equal to that. Let's try:
The sum of the remote interior angles is equal to the external angle.
I cannot see the question
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, we have
