



 
Hi Jessica. Draw a parabola on graph paper where the center of the bridge is at the origin and the cables rise up to to the points (±200, 75). Thus, the x axis is the road and the height of the parabola above the x axis (this would be the y value) reflects the height of the cable above the road surface. You know that the equation of a parabola that opens up is in the form y  y_{V} = a(xx_{V})^{2}, where (x_{V}, y_{V}) is the vertex (in this case, the origin) and a is just a constant that determines the curvature. Thus, the equation is y = ax^{2}. You need to find out what a is. To do this, you need to put the coordinates of a known point on the parabola (other than the vertex) into the equation in place of x and y and then solve for a. When you have the proper equation, you can substitute the value x = 100 and find the corresponding height of the cables above the road surface 100 m from the center of the road (the origin). If you do the arithmetic properly, you will indeed get 18.75 m. Cheers,  


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