Bonsoir,
[tex]f(x)=3x^2+5x-1\\\\
=-3(x^2-\dfrac{5}{3}x+\dfrac{1}{3})\\\\
=-3(x^2-2*\dfrac{5}{6}x+\dfrac{25}{36}-\dfrac{25}{36}+\dfrac{1}{3} )\\
=-3[(x-\dfrac{5}{6})^2-\dfrac{25}{36}+\dfrac{1}{3}]=\\\\
=-3[(x-\dfrac{5}{6})^2-\dfrac{13}{36}]=\\\\
=-3(x-\dfrac{5}{6})^2+\dfrac{13}{12}\\\\
[/tex]
