Question

Xác định hệ số a,b,c biết : (2x-5) . (3x+b) = ax^2+x+2

Answer 1

Sửa đề: \(\left(2x-5\right)\left(3x+b\right)=ax^2+x+c\)

Ta có:

\(\left(2x-5\right).\left(3x+b\right)=ax^2+x+c\)

\(\Leftrightarrow2x\left(3x+b\right)-5\left(3x+b\right)=ax^2+x+c\)

\(\Leftrightarrow6x^2+2bx-15x-5b=ax^2+x+c\)

\(\Leftrightarrow6x^2+\left(2b-15\right)x-5b=ax^2+x+c\)

\(\Rightarrow\left\{{}\begin{matrix}6x^2=ax^2\\\left(2b-15\right)x=x\\-5b=c\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}a=6\\b=8\\c=-40\end{matrix}\right.\)

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