Ta có:
` 2f(a) = g(a) `
` => 2a^2 = 3 - a `
` => 2a^2 + a - 3 = 0 `
` => 2a^2 - 2a + 3a - 3 = 0 `
` => 2a(a - 1) + 3(a - 1) = 0 `
` => (a - 1)(2a + 3) = 0 `
` => ` \(\left[ \begin{array}{l}a - 1=0\\2a+3=0\end{array} \right.\)
` => ` \(\left[ \begin{array}{l}a=1\\a=-\frac{3}{2}\end{array} \right.\)
Vậy ` a = 1 ` hoặc ` a = -3/2 ` thì ` 2f(a) = g(a) `