x(7 – x) 8

A.
2

B.
8

C.
–1

D.
0

Question

x(7 – x) > 8
 

  
 
 
 A.   
    2
   
  
 
 
 B.   
    8
   
  
 
 
 C.   
    –1
   
  
 
 
 D.   
    0

blurbendy · Answer

Start by distributing that x.
x(7 -x) > 8
7x + x^2 > 8
x^2 + 7x -8 > 0
(x+8)(x-1) > 0
x = -8
x = 1

blurbendy · Answer

Then substitute each back into the original equation, and see which one is true.

anonymous · Answer

For a problem like this, that you don't know how to solve, it is best to just pluge in the answers.
A 2= 10>8
B 8= -8>8
C -1= -8>8
D 0= 0>8
So there is only one true statement there and it is a

anonymous · Answer

where did the 10 come from?

zehanz · Answer

@Rosy95: there will be an occasion when there are no answers...
Therefore, it is always better to learn how to do such a problem (see @blurbendy's method), so next time you'll know what to do.

anonymous · Answer

10 is what you get on that side when you sub the 2 in for the x's.
x(7-x)>8
2(7-2)>8
14-4>8
10>8
@ZeHanz yes I know that, however I was just saying that when it comes down to a test you cant just look it up, therefore when they give you answer choice, plug it in

anonymous · Answer

@Rosy95 thanks

zehanz · Answer

@Rosy95: Am I right in thinking that a lot of people asking questions here do multiple choice questions all the time?

anonymous · Answer

Yes, and on math test it is a lot of mult choice questions, so if you are not getting something, plug it in and your welcome @d_poole

zehanz · Answer

That explains a lot. I'm from Holland, and many high school students never see even one multiple choice question at maths.

anonymous · Answer

Oh ok. Well to give you an example. I had a 40 question math test and only 3-5 were NOT multipul choice, so even if you miss the written ones, you will still pass.

zehanz · Answer

Advantage for the teacher: quick grading, although less rewarding if students are just trying some numbers, probably using a calculator...

anonymous · Answer

yes that is all true lol...and I am actually a tutor in algebra currently so I know how do these problems, but because someone had already explained how to do this problem, i was giving d_poole another option

anonymous · Answer

but @ZeHanz if you are good at precal or math in general can you help me with my question..here is the link to it on here http://openstudy.com/study#/updates/50f5c9aee4b061aa9f9ad656

zehanz · Answer

I'going to sleep now...sorry, but glad to help you soon! Bye.

anonymous · Answer

Ok. Thanks night!