1.

If x = sin14x + cos20 x, then write the smallest interval in which the value of x lie.

Answer»

We know the range of sin x is

-1 ≤ sin x  ≤ 1

∴ 0 ≤ sin 14x  ≤ 1

We know the range of cos x is

-1 ≤ cos x  ≤ 1

∴ 0 ≤ cos 20x ≤ 1

0 < sin14x + cos20x ≤ 2

which means that the value of x lies in the interval [0,2]

But there's a problem, when sine is 0 cosine is 1, they might even be 0 and -1 at particular points (not in this case, since they are even powers), so the minimum we would get should be more than 0. Hence the value of x lies in (0,1]



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