Mark the Correct alternative in the following:
If A = 2 sin2 x – cos 2x, then A lies in the interval
Given A = 2 sin2 x – cos 2x
[ using cos 2x = 1 – 2 sin2 x ]
so A = 2 sin2 x – cos 2x = 2 sin2 x –[ 1 – 2 sin2 x]
= 2 sin2 x -1 + 2 sin2 x]
= 4 sin2 x – 1
Now A = 2 sin2 x – cos 2x = 4 sin2 x – 1
As we know sin x lies between -1 and 1
-1 ≤ sin x ≤ 1
0 ≤ sin2x ≤ 1
Multiplying the inequality by 4
0 ≤ 4 sin2 x ≤ 4
Subtracting 1 from the inequality
-1 ≤ (4 sin2 x – 1) ≤ 3
From the above inequation, we can say that
A = (4 sin2 x – 1) belongs to the closed interval [-1,3]
Hence the answer is A.