Hàm số lượng giác

T

truongduong9083

Chào bạn

Ta có
[TEX]A = sin^4x+cos^4x =(sin^2x+cos^2x)^2-2sin^2xcos^2x = 1 - \frac{1}{2}sin^2{2x}[/TEX]
[TEX]\Rightarrow \frac{1}{2} \leq A \leq 1[/TEX]
nhé
Max A = 1 khi
[TEX]sin2x = 0 \Leftrightarrow x = k\frac{\pi}{2}[/TEX]
[TEX]Min A =\frac{1}{2}[/TEX] khi
[TEX]sin^2{2x} = 1 \Rightarrow cos2x = 0 \Leftrightarrow x = \frac{\p}{4}+k\frac{\pi}{2}[/TEX]
 
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