What is the minimum whole number of passengers who need to get off the elevator to meet the weight requirement

Aperpendicular bisector, cd is drawn through point con ab if the coordinates of point a are (-3, 2) and the coordinates of point b are (7,6), the x-intercept of cd is point lies on cd.

What is the missing step in this proof ?

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)