On interval 0 ≤ x < 2π, where are the x-intercepts of y = cos(2x)?
2 answers:
The answer is choice D because we plug in something like x = pi/4 and it leads to
y = cos(2x)
y = cos(2*pi/4)
y = cos(pi/2)
y = 0
Use the unit circle to see why cos(pi/2) = 0.
Since we get y = 0 as a result, this shows x = pi/4 is one of the x intercepts.
You'll also get y = 0 if you plug in x = 3pi/4, x = 5pi/4, and x = 7pi/4. All of these values are on the interval
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