The gradient of a straight line is equal to which value of its angle of inclination?

1. The angle of inclination is the angle a line makes with the positive horizontal direction. 2. Gradient is a vertical change divided by a horizontal change. 3. The tangent ratio is also one length divided by another in exactly that way. 4. So the gradient of a straight line equals the tangent of its angle of inclination. 5. Sine and cosine both divide by the hypotenuse instead, so neither matches the gradient. _Source: Siyavula Mathematics Grade 11 (Everything Maths, CC BY 4.0), Chapter 4: Analytical geometry_