f (x ) = cos^( 2) ( x ) + sin^( 4) ( x )
R_( f) = ?
−−−solution−−−
y = cos^( 2) (x ) + sin^( 2) (x) .( 1−cos^( 2) (x))
= 1 − (1/4) sin^( 2) ( 2x)
we know that :
0≤ sin^( 2) ( αx) ≤1
therefore
−1≤− sin^( 2) (2x) ≤ 0
1−(1/4) ≤ 1− (1/4) sin^( 2) (2x) ≤1
R_( f) = [ (3/4) , 1 ] ◂ ★ ▶
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