The height of a maintenance lift, H H\,H metres, relative to the ground floor is recorded over time t t\,t seconds. The height is modelled by the function
H(t)=18−∣3t−21∣ H(t) = 18 - |3t - 21| H(t)=18−∣3t−21∣Sketch the graph of H(t)H(t)H(t), marking the coordinates of any points where the graph intersects the axes and the coordinates of the vertex.
Solve the inequality
18−∣3t−21∣<9 18 - |3t - 21| < 9 18−∣3t−21∣<9
