Let S be the set of all α ∈ R such that the equation cos(2x) + α sin x = 2α − 7 has a solution. Then S is equal to:
[2, 6]
Using \(\cos 2x = 1-2\sin^2 x\) and letting \(s=\sin x\) (so \(s\in[-1,1]\)), the equation becomes \(1-2s^2+\alpha s = 2\alpha-7\).
Rearranging: \(8-2s^2+\alpha s-2\alpha=0\), i.e. \(\alpha(s-2) = 2s^2-8 = 2(s-2)(s+2)\).
Since \(s\in[-1,1]\), \(s-2\) is never zero, so dividing both sides gives \(\alpha = 2(s+2) = 2s+4\).
As \(s\) ranges over \([-1,1]\), \(\alpha=2s+4\) ranges over \([2(-1)+4,\ 2(1)+4] = [2,6]\).
So \(S=[2,6]\).
Similar Questions
The period of
\(\dfrac{|\sin 4x|+|\cos 4x|}{|\sin 4x-\cos 4x|+|\sin 4x+\cos 4x|}\) is:
The number of values of x lying in the interval (−π, π) which satisfy the equation 8^{1+|cos x|+cos²x+|cos³x|+....∞} = 4³ is:
Which of the following is greatest?
Important Questions from Trigonometric Functions
If \(\tan A=\dfrac{1}{7}\) , then what is cos 2A equal to?
What is tan 2A equal to?
What is the value of tan 18°?
What is the period of the function f(x) = ln(2 + sin 2x)?
If tan (45° + θ) = 1 + sin 2θ, where \(-\frac{\pi}{4}< θ <\frac{\pi}{4},\) then what is the value of cos 2θ?
