Need help with a maths q!

[Bugz]

I'm posting it here as a) it's a sat. morning and I don't want to wait till Monday and b) I am quite sure my answer is right and then answer in the back is wrong!


f(x) = 2x(squared) + px + q. Given that f(-3) = 0, and f(4) = 2:

a) find the value of p & q.

My Answer:

f(-3) = 2(-3)(Squared) + p(-3) + q = 0
=> 18 - 3p + q = 0
=> 18 = 3p - q


f(4) = 2(4)(Squared) + p(4) + q = 2
=> 32 + 4p + q - 2 = 0
=> - 30 = 4p + q

Putting both simultaneous equations together:

18 = 3p - q
+
-30 = 4p + q

=> -12 = 7p

According to the back this is wrong but i've triple checked and I see no mistakes.

Anyone? Rep on offer!

 

[Congax]

why the fuck are you doing math on a friday evening?

 

[liloe]

Yes, I come to the same conclusion and even the calculation is correct.

Equation 1:
  0 = 18 -3p +q
-18 = -3p +q

Equation 2:
      2 = 32 +4p +q |-32
    -30 = 4p +q     |-4p
-30 -4p = q

Putting 2 in 3:
     -18 = -3p +(-30 -4p)
     -18 = -3p -30 -4p
     -18 = -7p -30    |+30
      12 = -7p    |:7
  '12/7' = -p    |*(-1)
 '-12/7' = p

Putting p in 2:
q = -30 -4*(-'12/7')
q = -30 +'48/7'
q = -'162/7'


Now as check I tried the whole thing with f(4) = 2

  32 +4*('-12/7') +('-162/7')
= 32 -'48/7' -'162/7'
= 32 -'210/7'
= 32 -30
= 2

which is the correct result.

So basically I'm sure you're right there =)

 

[gohan]

f = pie

 

[kivik]

Got it to:

p = -12/7

q = -32 + 48/7

Most likely wrong in the back, happens sometimes. Or you were tired and checked the wrong answer

Besides, such newbie maths

 

[CorNokZ]

Math makes my head hurts.. I failed it so hard

 

[Congax]

Math makes my head hurts.. I failed it so hard

You wannebeeeee! Math makes my head hurt

 

[CorNokZ]

You wannebeeeee! Math makes my head hurt

Just because you're from Belgium doesn't mean you have to act like a prick

 

[Bugz]

Besides, such newbie maths

Give it a few months and it'll be much harder maths.

Further Maths is an insane speed. We covered ~20 pages of textbook work (one unit) in 3 hours .

 

[Agrigo]

I'm posting it here as a) it's a sat. morning and I don't want to wait till Monday and b) I am quite sure my answer is right and then answer in the back is wrong!


f(x) = 2x(squared) + px + q. Given that f(-3) = 0, and f(4) = 2:

a) find the value of p & q.

For F(-3): 0= 2(-3)^2 + p(-3) + q
0= 2(9) -3p + q
0= 18 -3p + q
-q= 18 -3p

For F(4): 2= 2(4)^2 + p(4) + q
2= 2(16) + 4p + q
2= 32 + 4p +q
2 - q = 32+4p

>>>>Sub in -q from F(-3)<<<<

2 + 18 - 3p = 32 + 4p
2 + 18 -32 = 4p + 3p
-12 = 7p
p = -12/7
p= -1.72

>>>> sub p into an equation <<<<

-q = 18 - 3p
-q = 18 - 3(1.72)
-q = 18 - 5.16
-q = 12.84
q = 12.84



theres the 2 answers, and thats how to do it iirc, numbers seem to be a bit to non whole so i porb made some calc error but i was using my head for division ;p

hope it helps

/Brian

>>>Sup p into one of the 2 pervious ones (F(-3) or F(4)

 

[Jugvayne]

Give it a few months and it'll be much harder maths.

Further Maths is an insane speed. We covered ~20 pages of textbook work (one unit) in 3 hours .

Have fun with FP2 and FP3 :touch:

 

[kivik]

We covered ~20 pages of textbook work (one unit) in 3 hours .

Got no idea how much that is

 

[Golena]

p = -1 and 5 7ths
q = 23 and 1 7th

or p = -1.714 (3sf)
q = 23.143(3sf)

Correct answer..
100% no question no matter what your book may say.

Unless it's actually written (2x)squared?

 

[fl3a]

Give it a few months and it'll be much harder maths.

Further Maths is an insane speed. We covered ~20 pages of textbook work (one unit) in 3 hours .

3 hours for 1 unit? i thought it was supposed to be a unit per lesson

 

[tris-]

3 hours for 1 unit? i thought it was supposed to be a unit per lesson

one unit per leson? our units at uni took all year last year!

 

[Bugz]

Seems the book is wrong.

Thanks for clarification all!

 

[Lamp]

You could always differentiate the leptokurtic manifold by using log-normal jump analysis and then normalising the errors with generalised auto-regressive conditional heteroskedasticity.

Easy.