Question

Interval of k for which, $f\left(x\right)=\sin x-\cos x-kx+b$ is decreasing for all real values -

• A. $(-\infty ,\sqrt{2})$
• B. $(\sqrt{2},\infty )$
• C. $(0,\infty )$
• D. $(-\sqrt{2},\sqrt{2})$

Answer 1

The correct option is B $(\sqrt{2},\infty )$

$f^{{}^{\prime }}\left(x\right)=\cos x+\sin x-k<0$
$k>\sin x+\cos x$
$k>\sqrt{2}$