Tìm đa thức \(f\left( x \right) = ax + b.\) Biết \(f\left( 1 \right) = \frac{7}{2};f\left( { - 1} \right) = - \frac{5}{2}.\)
A.\(f\left( x \right) = 3x + \frac{1}{2}\)
B.\(f\left( x \right) = x + \frac{1}{2}\)
C.\(f\left( x \right) = 3x + \frac{7}{2}\)
D.\(f\left( x \right) = 2x + \frac{1}{2}\)