1. The problem is to understand where the tangent function is in relation to sine and cosine. 2. Recall the definitions of sine and cosine for an angle $\theta$ in a right triangle or on the unit circle: $$\sin(\theta) = \frac{\text{opposite}}{\text{hypotenuse}}, \quad \cos(\theta) = \frac{\text{adjacent}}{\text{hypotenuse}}$$ 3. The tangent function is defined as the ratio of sine to cosine: $$\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}$$ 4. This means tangent measures the slope of the angle $\theta$ and can be thought of as the ratio of the opposite side to the adjacent side: $$\tan(\theta) = \frac{\text{opposite}}{\text{adjacent}}$$ 5. Important rule: tangent is undefined when $\cos(\theta) = 0$ because division by zero is not allowed. 6. So, tangent is not missing; it is derived from sine and cosine by division. Final answer: Tangent is given by $$\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}$$ and represents the ratio of sine to cosine.