Question
If A = sin2 x + cos4 x, then for all real x
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3/4 ≤ A ≤ 1
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31/16 ≤ A ≤ 1
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1≤ A ≤2
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3/4 ≤ A ≤ 13/16
Solution
A.
3/4 ≤ A ≤ 1
A = sin2x + cos4x = sin2x + (1 - sin2 x)
2 = sin4x - sin2x + 1