The greatest and least value of sinx cosx are
[MNR 1975]
1,-1
2,-2
Let f(x) = sin x cos x = 12 sin 2x
We know -1 ≤ sin2x ≤ 1 ⇒ - 12 ≤ 12 sin2x ≤ 12
Thus the greatest and least value of f(x) are 12 and - 12 respectively.