Answer:
![2√(5)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/jgyfqbamzskpd0akt906csriy4q01s27pv.png)
Explanation:
To add these vectors together, we have to "glue" them together.
Let's call the vector with the length of 2 A and the one with length 4 B.
Imagine you can grab vector A with your hands and move it to the end of B (it would look like the image that's annexed)
Now imagine that we made a triangle from that, what we want to know is the hypotenuse of that triangle!
We know that when we want to find the hypotenuse of a triangle, we can use Pythagoras theorem:
![h^2 = c_1^2 + c_2^2](https://img.qammunity.org/2021/formulas/mathematics/college/uakh1sqfq5qwq4di5ls4fwn0d2cek1wbd3.png)
Let's plug in the known values (the length of the vectors) and solve this
![h^2 = 2^2 + 4^2\\h^2 = 20 \\h = √(20)\\h = √(2\cdot 2\cdot 5)\\h = √(2^2 \cdot 5)\\h = 2√(5)\\](https://img.qammunity.org/2021/formulas/mathematics/college/rt7pqllzrqro8hzbdr3jeazny8x8wt5jm3.png)
Good luck!