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Câu hỏi: Đạo hàm của hàm số $y={{3}^{1-x}}$ bằng
A. $\dfrac{{{3}^{1-x}}}{\ln 3}$ .
B. ${{3}^{1-x}}.\ln 3$ .
C. $\left( 1-x \right){{.3}^{-x}}$ .
D. ${{3}^{1-x}}.\ln \left( \dfrac{1}{3} \right)$ .
A. $\dfrac{{{3}^{1-x}}}{\ln 3}$ .
B. ${{3}^{1-x}}.\ln 3$ .
C. $\left( 1-x \right){{.3}^{-x}}$ .
D. ${{3}^{1-x}}.\ln \left( \dfrac{1}{3} \right)$ .
${y}'={{\left( {{3}^{1-x}} \right)}^{\prime }}={{\left( 1-x \right)}^{\prime }}{{.3}^{1-x}}.\ln 3=-{{3}^{1-x}}.\ln 3={{3}^{1-x}}.\ln \left( \dfrac{1}{3} \right)$ .
Đáp án D.