Tìm m biết ∫m0(2x+5)dx=6

Question

Tìm m biết \(\int _{0}^{m}\left(2x+5\right){\rm d}x=6 \)

 A.\(m=-1;\, m=6 \).      B. \(m=1;\, m=-6.   \)

 C.\( m=-1;\, m=-6.\)      D. \(m=1;\, m=6.\)

Answer 1

Chọn B

Ta có : \(\int _{0}^{m}\left(2x+5\right){\rm d}x=6 \)
\(\begin{array}{l} {\Leftrightarrow \left. \left(x^{2} +5x\right)\right|_{0}^{m} =6} \\ {\Leftrightarrow m^{2} +5m-6=0} \\ {\Leftrightarrow \left[\begin{array}{l} {m=1} \\ {m=-6} \end{array}\right. } \end{array}\)