First Photo - This is the problem drawn into the paper. If you have two vectors and they form a right angle (90°) between them, the Resultant Vector will appear like this, from the right angle.
Obs.:
1 - VR = Resultant Vector;
2 - The angle formed by the VR and the two vectors ISN'T a bisector.
Second Photo - You can move the bottom extremity of the Y vector to the arrow of the X vector and the tips from the Y and VR vectors will meet, forming a Right Triangle, whose the VR is the Hypotenuse (Opposes the right angle / Larger Side).
Now you just put the values in the Pythagorean Theorem:
Where VR is the "a".
Obs.:
1 - VR = Resultant Vector;
2 - The angle formed by the VR and the two vectors ISN'T a bisector.
Second Photo - You can move the bottom extremity of the Y vector to the arrow of the X vector and the tips from the Y and VR vectors will meet, forming a Right Triangle, whose the VR is the Hypotenuse (Opposes the right angle / Larger Side).
Now you just put the values in the Pythagorean Theorem:
Where VR is the "a".