Engineering
Mathematics
Maxima and Minima
Question

The function f(x) = 2 | x | + | x + 2 | – | |x + 2| –2 |x| | has a local minimum or a local maximum at x =

2

 23

 23

– 2

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Solution

x > 0

            f (x) = 2x + x + 2 – | 2 – x |

            x  2

            2x + x + 2 – x + 2 = 2x + 4

            0  x < 2

            2x + x + 2 – 2 + x = 4x

            x  – 2

            f (x) = – 2x – x – 2 – | – x – 2 + 2x |

                    = – 3x – 2 – | x – 2 |

                    = – 3x – 2 + x – 2 = – 2x – 4

            – 2 < x < 0

            f (x) = – 2x + x + 2 – | x + 2 + 2x |

                    = – 2x + x + 2 – | 3x + 2 |

            – 2 < x <  23                         23  < x < 0

            – 2x + x + 2 + 3x + 2               – 2x + x + 2 – 3x – 2

            2x + 4                                      – 4x