Quadratic Equations

[LoreneTJ]

Hello, I could use some help with a quadratic equation.
neg 4xsquare minus 6x + 2. x=neg3/4
The book says the answer is 17/4 but I'm not even close! I've worked out:
neg 4(9/16) minus 6(neg 3/4) + 2
neg 73/16 + 108/16 + 2
35/16 + 32/16
= 67/16

Please help!
thanks,
LoreneTJ

 

[Denis]

neg 4xsquare minus 6x + 2. x=neg3/4
The book says the answer is 17/4 but I'm not even close! I've worked out:
neg 4(9/16) minus 6(neg 3/4) + 2
neg 73/16 + 108/16 + 2
35/16 + 32/16
= 67/16

Post like this: -4 x^2 - 6x + 2

-4 (9/16) = -36/16 : HOW did you ever get -73/16 ?

-6(-3/4) = 72/16 : HOW did you ever get 108/16 ?

SO: -36/16 + 72/16 + 2 = finish it...

 

[mmm4444bot]

… I could use some help with a quadratic equation.

neg 4xsquare minus 6x + 2. <<<< This is not an equation.

-4x^2 - 6x + 2 is a quadratic polynomial.

(All equations contain an equal sign!)

x=neg3/4 <<<< Write this as x = -3/4.

neg 4(9/16) minus 6(neg 3/4) + 2

neg 73/16 + 108/16 + 2

35/16 + 32/16

= 67/16

So, you're not trying to solve a quadratic equation; you are trying to evaluate a quadratic polynomial for x equal to -3/4.

It looks like you made the substitution for x correctly, and you correctly squared -3/4.

After that, it looks like you made a lot of arithmetic mistakes with fractions.

-4(9/16) - 6(-3/4) + 2

-4 times 9 is -36, not -73.

Do you know?

Instead of multiplying -4 times 9, you can cancel that 4 with a factor of 4 in the denominator because 16 is 4^2.

-9/4 - 6(-3/4) + 2

-6 times -3 is 18.

-9/4 + 18/4 + 2

2 is equal to 8/4.

-9/4 + 18/4 + 8/4

(-9 + 18 + 8)/4

17/4

I think you need to review arithmetic with fractions. People who try to learn algebra without knowing how to work with fractions should expect to experience a lot of frustration.