tank game, rotation & direction/angle, with Raylib C

Rotated rectangle drawing is done by "DrawRectanglePro(Rectangle rec, Vector2 origin, float rotation, Color color);". Rotation and how it relates to the object's position is a sort of "black box" for me at the moment. Direction/Angle described and translated between degree, radian, normalized vector, vector. vector ---(Pythagorean theorem, a^2+b^2=c^2, a/c, b/c, vector scaled to a unit of magnitude/length_of_hypotenus)--- normalized vector ---(cosf(angle), sinf(angle))--- degree ---(multiplying by PI/180, 180/PI)--- radian (a unit = the radius, PI = ratio between circumference and half a circle). magnitude/speed is set to 1 for both rotation and movement. rotation variable tank rotates. turret rotates with tank and without tank. bullet rotates with turret. position/movement variable bullet moves to the tip of the rotated turret. bullet moves in the turret's rotated direction. tank moves forward and backward in the rotated direction.