Trigonometry: Grade of a Road

The grade of a road is the tangent of the angle of that surface to the horizontal. If the grade is 0% then there is no slope, but the greater the % the higher/steeper the degree of tilt is. Knowing the grade of a road is important for cars because they have something called the gradeability. The gradeability of a car is the highest grade a car can go at a certain speed. So if the grade is high the driver then knows that they have to go a greater speed to prepare for the steep hill.

The grade of a road is equal to the slope of a line. Also, the grade of a road is equivalent to the hypotenuse of a triangle, so if we can use trigonometry to find the hypotenuse we can use trigonometry to find the grade of a road.