# Finding the vertex of a quadratic and the product of two complex numbers

#### drop

##### New member
Basically I don't know anyone in real life that can help me with this, so I need help checking to see if my answers are correct PART A

11) Find the vertex of f(x) = -2x^2 - 8x + 3 algebraically.

12) Multiply and simplify: (6 - 5i) (4 + 3i)

#### anemone

##### MHB POTW Director
Staff member

Basically I don't know anyone in real life that can help me with this, so I need help checking to see if my answers are correct PART A

11) Find the vertex of f(x) = -2x^2 - 8x + 3 algebraically.

I get $(-2, 11)$. Now can you help me by explaining to us how did you arrive at $(-2, 0)$ as the vertex of the function of f of x?

12) Multiply and simplify: (6 - 5i) (4 + 3i)

Correct. #### drop

##### New member

x = -b/(2a)

x = -(-8)/2(-2)

x = 8/-4 = -2

I think I forgot to substitute -2 for x to find out y, thanks for pointing that out! (I was thinking of x intercepts) After solving for y, I got (-2,11) Thank you

#### anemone

##### MHB POTW Director
Staff member
Yes...and as you can see, $f(-2)=-2(-2)^2-8(-2)+3=11$.