Question: How can I validate if an object is of a certian class? I currently use 

```
get_class($obj) == 'User';

```

But it may look like `\KM\User` when I am elsewhere? I think this way maybe abit prone to developer error. Is there something like:

```
compare_class($obj1, User);
// or maybe
classof($obj) == User;

```

Answer: 
You can simply compute verything before:

plot 25-20+((2Pi0.3²)/(Pi10²)Sqrt[2\*980(1+(Pi10²)/(Pi10²))]t)² from 0 to 38

or

plot 25-20+((2\*0.3²)/(10²)Sqrt[2\*980(1+1)]t)² from 0 to 38

or 

25 - 20 + 4 \* 0.0000081 \* 3920\*t^2 from 0 to 38 (I have some factor wrong, but you get the idea)

just apply basic math to the constants and remove the middle (imaginary part) after applying the 2nd binomic formula.

There is nothing to do with complex numbers.
The square root of an integer is going to be an integer or a complex number whose real part is zero. The real part of the square root of a negative integer is zero. Always.

So ...

```
public double realPartOfSquareRoot(int i) {
    return (i > 0) Math.sqrt(i) : 0;
}

```

---

> 
> But how I solve this? If I replace the squareroot by 0, I don't get a good result. Do I suppose the imaginary part do something on the real with the rest of the formula.
> 
> 
> 

I expect that's so! (The idea of discarding the imaginary part didn't make much sense to me ... but I assumed you had a sound reason to do this.)

The real answer is to find a Java library that will do complex arithmetic. I've never needed to use it, but the first one to examine should be the [Apache Commons Maths](http://commons.apache.org/math/userguide/complex.html) library.