Problem

Here are the graphs of four functions. The equations of the graphs are \[y=f(x) \quad y=f(x)-8 \quad y=3f(x) \quad \text{and} \quad y=3f(x)+8.\]

Plots of the four functions above with a point on each being highlighted as A, B, C, D.
  • The \(x\)-coordinates of \(A\), \(B\), \(C\) and \(D\) are all the same. What can you deduce about the gradients of the curves at \(A\), \(B\), \(C\) and \(D\)?

  • The gradient of the tangent at \(D\) is \(\tfrac{1}{4}\). What are the gradients of the tangents at \(A\), \(B\) and \(C\)?


Here are the graphs of another four functions. The equations of these graphs are \[y=f(x)\quad y=f(x+20)-8 \quad y=3f(x-25) \quad \text{and} \quad y=-3f(x)+10.\]

Plots of the four functions above with a point on each being highlighted as E, F, G, H.
  • The \(x\)-coordinates of points \(E\), \(F\), \(G\) and \(H\) are \(-15\), \(5\), \(5\) and \(30\) respectively. What can you deduce about these points?

  • The gradient of the tangent at \(E\) is \(-\tfrac{1}{4}.\) What are the gradients of the tangents at \(F\), \(G\) and \(H\)?