How do you find all extrema in the interval [0, 2(pi)] for #y= sin x + cos x#?

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Answer 1 · 2015-04-16T00:21:37

#y = sin x + cos x = sqrt2*sin (x + pi/4).#
#sin (x + pi/4)# has max at #(1)# and #(-1)#.
Then, #y# has max at #(sqrt2)# and #-(sqrt2).#