Notice when we drew the velocity vector for our Smart Car, we also put in two smaller arrows. These arrows point exclusively in the **x and y directions**, and are the **x and y components** of the velocity vector. These components make a triangle with the velocity vector, which is the hypotenuse.

The mathematical study of triangles is called **trigonometry**, and one thing trigonometry is useful for is working with vectors. Even if you don’t know trigonometry, you’ve probably messed with the **SIN**, **COS**, and **TAN** buttons on a calculator. We can use the definition of a cosine (COS) to find the length of the **x-component**. *On a calculator, type in 30, hit COS, and multiply that number by the hypotenuse (45 mph)*. You find that **in the x direction only, the car is moving 39 mph.**