# Thread: quick question, need bit of help

1. ## quick question, need bit of help

looking at an example i jotted off the white board today,

C = 550 - 10X + (1/2)X^2

R = 75X - (1/2)X^2

Then Ive written P= R - C which is...

P = 85X - X^2 - 550

but i just jotted the answer, i get how ive got 85x but cant remember how to get the 1/2 x^2 into just -x^2

if someone could go throught the question that would be great,

Thank you.

2. Originally Posted by bobchiba
looking at an example i jotted off the white board today,

C = 550 - 10X + (1/2)X^2

R = 75X - (1/2)X^2

Then Ive written P= R - C which is...

P = 85X - X^2 - 550

but i just jotted the answer, i get how ive got 85x but cant remember how to get the 1/2 x^2 into just -x^2

if someone could go throught the question that would be great,

Thank you.
$\displaystyle 75x-\frac{1}{2}x^2-\left(550-10x+\frac{1}{2}x^2\right)=$

$\displaystyle 75x{\color{red}-\frac{1}{2}x^2}-550+10x{\color{red}-\frac{1}{2}x^2}=$

$\displaystyle 85x{\color{red}-x^2}-550$

3. Originally Posted by bobchiba
looking at an example i jotted off the white board today,

C = 550 - 10X + (1/2)X^2

R = 75X - (1/2)X^2

Then Ive written P= R - C which is...

P = 85X - X^2 - 550

but i just jotted the answer, i get how ive got 85x but cant remember how to get the 1/2 x^2 into just -x^2

if someone could go throught the question that would be great,

Thank you.
$\displaystyle -\frac{1}{2}x^2- \frac{1}{2}x^2= -(\frac{1}{2}+ \frac{1}{2})x^2= -x^2$
Because 1/2+ 1/2= 1!