Show that the curve y = (3x² + 8)² has only one stationary point. Find the coordinates of this stationary point and determine its nature.
- Show that the curve y = (3x² + 8)² has only one stationary point. Find the coordinates of this stationary point and determine its nature.[8]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [M1] differentiation to obtain answer in the form p(3x² +8) or qx(3x² +8)
- [B1] 6x(3x² +8)
- [A1] dy/dx = 12x(3x² +8) all correct
- [DM1] When dy/dx = 0 only solution is x = 0 qx(3x² +8) = 0 and attempt to solve
- [A1] x=0 and 3x² +8 = 0 has no solutions
- [A1] Stationary point at (0,32)
- [M1] correct gradient method with substitution of x values either side of zero or equivalent valid method
- [A1] correct conclusion from correct work using a correct dy/dx
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