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Help maths transformations

Help, part C
I don’t get where the inequalities circled come from/ how to work them out plz help!! Since that’s what I need to write to get marksIMG_2228.jpegIMG_2229.jpeg
(edited 1 year ago)
You must read the question/model solution? The second derivative is -sin(x) you want that to be < 0 or >0 for concave or convex. The range of values of x for which -sin(x) is < 0 or > 0 should be clear?
(edited 1 year ago)

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