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Loch Ness

Age 16 to 18
Challenge Level

monsters
(1) Plot the graph of the function $y=f(x)$ where $f(x) = \sin x +|\sin x|$. Find the first derivative of this function and say where it is defined and where it is not defined.

(2) Express the function $f(x) = \sin x + \cos x$ in the form $f(x)=A\sin (x+\alpha)$, find $A$ and $\alpha$ and plot the graph of this function. Similarly express the function $g(x) = \sin x - \cos x$ in the form $g(x) = B\sin (x +\beta)$ where $-\pi /2 < \beta < \pi /2$, and plot its graph on the same axes.

(3) Plot the graph of the function $y=f(x)$ where $f(x)= \sin x + |\cos x|$. Find the first derivative of this function and say where it is defined and where it is not defined.


NOTES AND BACKGROUND
These graphs are not monsters. They are humpy because the functions are periodic and involve sines, cosines and absolute values. This problem calls for you to describe and explain the features of the graphs.

First think about the features of the graphs and try to sketch them for yourself, then it may help to use a graphic calculator or graphing software.

Andrei from Romania chose this problem for the NRICH 10th Anniversary special collection. He said "The problems you are posting on the site are usually, at least for me, far from the problems we solve in school or in other activities related to school."

We would like to hear from other students. Is this your experience?

Andrei says "It's a difficult task to choose the problems I liked most, and to choose one seems impossible." So he also chose Over-booking and Wobbler.

The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
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