$\left\{\begin{array}{l}a=6 \\ b=8 \\ c=-40\end{array}\right.$ | |
$\left\{\begin{array}{l}a=6 \\ b=-8 \\ c=-40\end{array}\right.$ | |
$\left\{\begin{array}{l}a=-6 \\ b=8 \\ c=-40\end{array}\right.$ | |
$\left\{\begin{array}{l}a=6 \\ b=8 \\ c=40\end{array}\right.$ |
Chọn phương án A.
Ta có: $(2x−5)(3x+b)=6x^2+2bx-15x-5b=6x^2+(2b-15)x-5b$
Mà $(2x−5)(3x+b)=ax^2+bx+c$
Nên $\left\{\begin{array}{l}a=6 \\ b=2b-15 \\ c=-5b\end{array}\right. \Leftrightarrow \left\{\begin{array}{l}a=6 \\ b=8 \\ c=-40\end{array}\right.$