# How do you figure this out, can you help me please??

• Jun 9th 2008, 04:15 AM
sweetbinti
How do you figure this out, can you help me please??
I have real problems trying to figure this out, as I was not in class when er learned this. Does anyone know how to??
Ok so here is the question:

21d*d+8d-26= 0

What are the steps that you have to take???
Thank you so much for helping me
seetbinti(Doh)
• Jun 9th 2008, 04:24 AM
topsquark
Quote:

Originally Posted by sweetbinti
I have real problems trying to figure this out, as I was not in class when er learned this. Does anyone know how to??
Ok so here is the question:

21d*d+8d-26= 0

What are the steps that you have to take???
Thank you so much for helping me
seetbinti(Doh)

$\displaystyle 21d^2 + 8d - 26 = 0$

The quickest approach is the quadratic formula.

-Dan
• Jun 9th 2008, 09:01 AM
ice_syncer
Quote:

Originally Posted by sweetbinti
I have real problems trying to figure this out, as I was not in class when er learned this. Does anyone know how to??
Ok so here is the question:

$\displaystyle 21d*d+8d-26= 0$

What are the steps that you have to take???
Thank you so much for helping me
seetbinti(Doh)

$\displaystyle 21d*d+8d-26= 0 is also written as 21d^2+8d-26= 0$

now you can factorize this equation or as the above guy said use the quadratic formula, but assuming you don't know it I'll show you the factorizing method !!!

so , $\displaystyle 21d^2 + 8d - 26 = 0$

we can't split middle term so we do it by completing the square or by converting it to the form (a+b)^2 = 0

so, we first transpose -26 to the RHS

so we get

$\displaystyle 21d^2 + 8d = 26$

we no divide the whole equation by 21 to x^2 coefficient to a perfect square and 1 is a perfect square.

so we get

$\displaystyle d^2 + 8/21d = 26/21$

can be written as

$\displaystyle d^2 + 2(1)(4/21) = 26/21$

no we add (4/21)^2 to both sides just to make the whole expression (a^2 + 2ab + b^2)ish

so,

$\displaystyle d^2 + 2+(1)(4/21) + (4/21)^2 = 26/21 + (4/21)^2$

factorizing LHS we get

$\displaystyle (d+4/21)^2 = 26/21 + 16/441$

$\displaystyle (d+4/21)^2 = (546 + 16)/441$

$\displaystyle (d+4/21)^2 = 562/441$
$\displaystyle d+4/21$ = PLUS OR MINUS $\displaystyle Sqrt(562)/21$

$\displaystyle d$ = PLUS OR MINUS$\displaystyle Sqrt(562)/21 - 4/21$

and thats the solution.

Ice Sync

(Emo)
• Jun 9th 2008, 09:14 AM
masters
Quote:

Originally Posted by topsquark
$\displaystyle 21d^2 + 8d - 26 = 0$

The quickest approach is the quadratic formula.

-Dan

What he said!!

$\displaystyle d=\frac{-4\pm\sqrt{562}}{21}$