Q51 ans a
take g(x) = f(x)- sin x
now g(0) , g(pi/2) and g(3pi/2) =0.
apply rolle to get c1, c2 whr g’ is 0.
now aplly rolle on g’ in interval (c1,c2).
then g” is zero. so f”(c)= -sin c hence
|f”(c) |< 1
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