\(P=\dfrac{1}{2}\cdot\dfrac{-3}{7}+\dfrac{2}{3}\cdot\dfrac{-3}{7}+\dfrac{3}{2}\cdot\dfrac{-3}{7}=\dfrac{-3}{7}\left(\dfrac{1}{2}+\dfrac{2}{3}+\dfrac{3}{2}\right)=\dfrac{-3}{7}\cdot\dfrac{8}{3}=\dfrac{-8}{7}\)
\(P=\dfrac{1}{2}a+\dfrac{2}{3}a+\dfrac{3}{2}a\\ =\left(\dfrac{1}{2}+\dfrac{2}{3}+\dfrac{3}{2}\right)a\\ =\dfrac{8}{3}a\\ =\dfrac{8}{3}.\left(-\dfrac{3}{7}\right)\\ =\dfrac{-8}{7}\)
Thay a = -3/7 vào P ta được
\(P=\dfrac{1}{2}a+\dfrac{2}{3}a+\dfrac{3}{2}=\dfrac{8}{3}a\Rightarrow P=\dfrac{8}{3}\left(-\dfrac{3}{7}\right)=-\dfrac{8}{7}\)
\(P=\dfrac{1}{2}a+\dfrac{2}{3}a+\dfrac{3}{2}a\)
\(=2a+\dfrac{2}{3}a\)
\(=\dfrac{8}{3}a\)
Tại x=\(-\dfrac{3}{7}\) , giá trị của biểu thức là :
\(\dfrac{8}{3}\cdot\left(-\dfrac{3}{7}\right)=-\dfrac{8}{7}\)
Thay a = \(-\dfrac{3}{7}\) vào biểu thức, ta có:
\(\dfrac{1}{2}.\left(\dfrac{-3}{7}\right)+\dfrac{2}{3}.\left(\dfrac{-3}{7}\right)+\dfrac{3}{2}.\left(\dfrac{-3}{7}\right)\)
\(=\left(\dfrac{-3}{7}\right).\left(\dfrac{1}{2}+\dfrac{2}{3}+\dfrac{3}{2}\right)=\dfrac{-8}{7}\)
Vậy giá trị của biểu thức \(P=\dfrac{1}{2}a+\dfrac{2}{3}a+\dfrac{3}{2}a\) bằng \(\dfrac{-8}{7}\) tại \(a=\dfrac{-3}{7}\)
