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Meant to be Off topic! Sorry 

Nice one! 

x^2 + ax + 1  = x^2 - x - a

ax + 1  = -x - a

ax + x  =   -1 - a

x(1 + a)  =  - ( 1 + a)

x =   - (1 + a)

       _______

           (1 + a)

x = - 1    is the common root        [if a not equal to -1 ]

Therefore  using the first function

(-1)^2 + a(-1) + 1  = 0                     

1 - a + 1  = 0

2 - a  = 0

a = 2

And using the second function as a check

(-1)^2  - (-1) - 2  = 0     ???

1 + 1 - 2  = 0

2 - 2  = 0   true

Please Thank killersteve27 for this message I copied it from him he really on how to welcome people! '

Thanks killersteve27

Welcome Annelito, and victor.gomez1

Nice job did you like mine do you think it is right I belive so! 

1. A group of 25 high school students were asked whether they use either Facebook or Twitter or both,Fifeen of these students use facebook and twelve use Twitter

A.How many use facebook only?

B. How many use twitter pn;y?

C. How many use both social networking sites?

Those using Facebook + Those using Twitter  - Total Number of Students  = Number using both

15  + 12  - 25  =   2

Here is the Venn diagram :

Facebook only  = 13

Twitter only  = 10

Both  =  2

Okay HiylinLink I think she got it from problem 1 

I would wait though guest Cphill a mod might have a better explanation! 

Thank you so much!

I just hope that it is correct...LOL!!!!

Nice one that is a hard question by the looks of all the work your showing good job! 

It is a very confusing question HiylinLink the guest was struggling to figure out the answer it took me a few minutes to solve! 

Let the roots be  R,  R + D  , R + 2D

So....by Vieta.....

R + (R +D) + (R + 2D)  = 15

3R + 3D  = 15

3 (R + D)  = 15

R + D  = 5

D = 5 - R

2D = 10-2R

And 

R( R + D) + R(R + 2D) + (R+D)(R+2D)  =  40

R[5 ] + R [R + 10 -2R] + [5] [ R + 10 - 2R ] = 40

5R + R[10 -R] + 5[ 10-R]  = 40

5R + 10R - R^2 + 50 - 5R  = 40

-R^2 + 10R + 50  = 40

-R^2 + 10R + 10  = 0

R^2 - 10R - 10  = 0

R^2 - 10R + 25 =  10 + 25

(R - 5)^2  =  35

R  =   5 + √35       or       R  = 5 - √35

So

If R = 5 + √35                or            If  R = 5 - √35

D = -√35                                            D = √35

And   R(R+D)(R + 2D)  =  -c

So  either

(5 + √35) (5) (5  - √35)   = -c         or       (5- √35) (5) (5 + √35)  = -c

(25 - 35)(5) = -c                                       (25 - 35) (5)  = -c

(-10)(5)  = -c                                            (-10)(5)  = - c

-50 = -c                                                       -50  = -c

50  = c                                                         50  = c

So

c  = 50

Problem 2 

A. 36  totall        Becuse first 24 students went to coron then 12 more is 36 students 

B. Well first 18 students went to Tubbatona then 12 more came to Tubbatona so 30 in totall visited Tubbatona

C. 11 made a trip to El nido Because look in the text (11 made a trip to coron and el nido )   and 20 visited only see (20visited El Nido)

D. so it says 10 seen the three tourist spots and there are 50 students so 50-10=40 so 40 didnt! 

Hope I did not take to long hope this helps to! 

Ok thank you so much

Thats fine 2 is tricky HiylinLink

There is alot of groups 

Im sorry

Sort them out with this

The no.2 please im girl I got the the no.1 please

The left is for students who only use Facebook the Middle  is for students who use both twitter and facebook the right is for students who only use twitter Got it tell me what you get for problem 1