Does the graph of y = sin(x - sinx) have horizontal tangents at the x-axis?

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Geeganage W2012-05-10T23:54:21Z

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y = sin(x - sinx)
dy/dx ={cos(x-sinx)]*(1-cosx)
when dy/dx=0;
cos(x-sinx)=0 or cosx=1
when cosx=1;
x=2nπ, where n is an integer
Then y = 0
Therefore the graph of y = sin(x - sinx) have horizontal tangents at the x-axis for all x =2nπ