sửa đề
Tìm a,b biết f(1)=g(2) và f(-1)=g(5)
\(f\left(1\right)=2.1^2+a.1+4\)
\(=2+a+4\)
\(=a+6^{\left(1\right)}\)
\(g\left(2\right)=2^2-5.2+b\)
\(=4-10+b\)
\(=-6+b^{\left(2\right)}\)
\(=b-6\)
\(f\left(-1\right)=2\left(-1\right)^2+a\left(-1\right)+4\)
\(=2-a+4\)
\(=6-a^{\left(3\right)}\)
\(g\left(5\right)=5^2-5.5+b\)
\(=25-15+b\)
\(=b^{\left(4\right)}\)
Từ \(\left(1\right)\left(2\right)\left(3\right)\left(4\right)\Rightarrow\hept{\begin{cases}6+a=-6+b^{\left(1'\right)}\\6-a=b^{\left(2'\right)}\end{cases}}\)
Từ (1') (2') ta có \(6+a=-6+6-a\)
\(6=-2a\)
\(\Rightarrow a=-3\)
\(b=6-\left(-3\right)\)
\(b=9\)