Moderate -0.5 This is a straightforward application of the perpendicularity condition for planes: normal vectors must be perpendicular, so their dot product equals zero. It requires only one calculation step (dot product = 0) and solving a simple linear equation, making it easier than average despite being from Further Maths.
2 The plane $x + 2 y + c z = 4$ is perpendicular to the plane $2 x - c y + 6 z = 9$, where $c$ is a constant. Find the value of $c$.
\hfill \mbox{\textit{OCR MEI Further Pure Core 2019 Q2 [3]}}