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Lời giải:
$y=\sqrt{\cos(x^2+2x+3)}$
$y'=\frac{-(x+1)\sin (x^2+2x+3)}{\sqrt{\cos (x^2+2x+3)}}$
y ' = ( sin x + cos x ) ' y ' = ( sin x ) ' + ( cos x ) ' = c osx - sinx
Chọn đáp án C
\(y'=\left(cosx\right)'\\ =\left(\dfrac{\pi}{2}-x\right)'cos\left(\dfrac{\pi}{2}-x\right)\\ =-cos\left(\dfrac{\pi}{2}-x\right)\\ =-sinx\)
a: \(y'=\left(x^2-x\right)'=2x-1\)
\(y''=\left(2x-1\right)'=2\)
b: \(y'=\left(cosx\right)'=-sinx\)
\(y''=\left(-sinx\right)'=-cosx\)
\(\begin{array}{l}f'({x_0}) = \mathop {\lim }\limits_{x \to {x_0}} \frac{{f(x) - f({x_0})}}{{x - {x_0}}} = \mathop {\lim }\limits_{x \to {x_0}} \frac{{\cos x - \cos {x_0}}}{{x - {x_0}}} = \mathop {\lim }\limits_{x \to {x_0}} \frac{{ - 2\,.\,\sin \frac{{x + {x_0}}}{2}.\sin \frac{{x - {x_0}}}{2}}}{{x - {x_0}}}\\ = \mathop {\lim }\limits_{x \to {x_0}} \frac{{ - 2.\frac{{x - {x_0}}}{2}.\sin \frac{{x + {x_0}}}{2}}}{{x - {x_0}}} = \mathop {\lim }\limits_{x \to {x_0}} \,\left( { - \sin \frac{{x + {x_0}}}{2}} \right) = - \sin \frac{{2{x_0}}}{2} = - \sin {x_0}\\ \Rightarrow f'(x) = (\cos x)' = - \sin x\end{array}\)
\(y'=2021\cdot cos\left(x\sqrt{x}\right)^{2020}\cdot\left(cos\left(x\sqrt{x}\right)\right)'\)
\(=2021\cdot\left(-x\sqrt{x}\right)'\cdot sin\left(x\sqrt{x}\right)\cdot cos\left(x\sqrt{x}\right)^{2020}\)
\(=-2021\cdot\dfrac{\left(x^3\right)'}{2\sqrt{x^3}}\cdot sin\left(x\sqrt{x}\right)\cdot cos^{2020}x\sqrt{x}\)
\(=-2021\cdot\dfrac{3x^2}{2x\sqrt{x}}\cdot sin\left(x\sqrt{x}\right)\cdot cos^{2020}x\sqrt{x}\)
\(=-\dfrac{6063}{2}\sqrt{x}\cdot sin\left(x\sqrt{x}\right)\cdot cos^{2020}x\sqrt{x}\)
Tại sao là x^3 vậy bạn?