MCQ
If $f(x) = a\cos (bx + c) + d$, then range of $f(x)$ is
  • A
    $[d + a,\;d + 2a]$
  • B
    $[a - d,\;a + d]$
  • C
    $[d + a,\;a - d]$
  • $[d - a,\;d + a]$

Answer

Correct option: D.
$[d - a,\;d + a]$
d
(d) $f(x) = a\cos (bx + c) + d…..(i)$

For minimum $\cos (bx + c) = - 1$

from $(i)$, $f(x) = - a + d = (d - a)$

For maximum $\cos (bx + c) = 1$

from $(i)$, $f(x) = a + d = (d + a)$

$\therefore$ Range of $f(x) = [d - a,\,\,d + a]$

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