Hi :) I don’t understand the inequality part ... anyone able to help? Thank you :)!
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Completing the square gives
[tex]x^2+3x-6=x^2+3x+\dfrac94-\dfrac{33}4=\left(x+\dfrac32\right)^2-\dfrac{33}4[/tex]
Then
[tex]f(x)=\left(x+\dfrac32\right)^2-\dfrac{33}4\ge0-\dfrac{33}4=-\dfrac{33}4[/tex]
and -33/4 = -8.25, so your answer is correct.