Thread: quadratic equations with fractions

1. quadratic equations with fractions

I can't understand how I can find the X's here...
(x-4)(30/x+2)=30

Thanks

2. Originally Posted by dgolverk
I can't understand how I can find the X's here...
(x-4)(30/x+2)=30

Thanks
Expand the brackets:

$
(x-4)(30/x+2)=30+2x-\frac{120}{x}-8=30
$
.

Simplify a bit:

$
2x-\frac{120}{x}-8=0
$
.

Multiply through by $x$:

$
2x^2-8x-120=0
$
.

Now use the quadratic formula to solve for $x$

RonL

3. well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
the book's answer is wrong? or I did something not right?

4. Originally Posted by dgolverk
well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
the book's answer is wrong? or I did something not right?
Hello,

the bad news first: The answers in your book are right. Maybe you can demonstrate what you've done. Then it's much easier to help you.

Greetings

EB

5. Originally Posted by dgolverk
well, it's the same way that I tried, but my answer isn't right according the answers book - it says that X=10 and X=-6
the book's answer is wrong? or I did something not right?
Hello,

that's what you should have done: Use the quadratic formula:

$x=\frac{-(-8) \pm \sqrt{64-4 \cdot 2 \cdot(-120)}}{2\cdot 2}$

$x=\frac{-(-8) \pm \sqrt{64+960}}{2\cdot 2}$

$x=\frac{-(-8) \pm 32}{2\cdot 2}$

$x=\frac{40}{4}\ \vee \ x=\frac{-24}{4}$

Greetings

EB

6. intersting...

I did exactly what you have done and got other answers..I guess I forgot something
Thanks a lot!