fp1 complex numbers

OP

Original post by B_9710

If x=1/2 is a solution then (2x-1) is a factor of the cubic.
Algebraic division is the way forward.

that's what i did but it doesn't work eventually i just get x^2 -4x+2 which doesn't give be a complex conjugate, it just gives me root 2 +2

so you'll be asking for my workings

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Reply 62

B_9710

18

Original post by timebent

that's what i did but it doesn't work eventually i just get x^2 -4x+2 which doesn't give be a complex conjugate, it just gives me root 2 +2

so you'll be asking for my workings

Your very last step when doing algebraic division is wrong. You should get the quotient to be

x^2-4x+13

.

Reply 63

OP

Original post by B_9710

Your very last step when doing algebraic division is wrong. You should get the quotient to be

x^2-4x+13

.

oh -.-' everytime....

Reply 64

OP

Original post by B_9710

Your very last step when doing algebraic division is wrong. You should get the quotient to be

x^2-4x+13

.

http://www.examsolutions.net/a-level-maths-papers/Edexcel/Further-Maths/Further-Maths-FP1/2013-January/paper.php#Q5
i decided to start with the left bracket.

So i tried to solve for x and see what i'd get, since the question told me there'll be 2 conjugate pairs in total i should get 1 pair from this bracket on the left.

4x^2 +9=0[br][br]4x^2=-9[br][br]x^2=-\frac{9}{4}[br][br]x=\sqrt {-\frac{9}{4}}

Reply 65

Sorry I was out.

ImageUploadedByStudent Room1469211240.697405.jpg

Reply 66

Original post by timebent

http://www.examsolutions.net/a-level-maths-papers/Edexcel/Further-Maths/Further-Maths-FP1/2013-January/paper.php#Q5
i decided to start with the left bracket.

So i tried to solve for x and see what i'd get, since the question told me there'll be 2 conjugate pairs in total i should get 1 pair from this bracket on the left.

4x^2 +9=0[br][br]4x^2=-9[br][br]x^2=-\frac{9}{4}[br][br]x=\sqrt {-\frac{9}{4}}

Basically, anything which is negative and is square rooted.
It is basically, that number square rooted i.

I'll post examples wait.

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Reply 67

Original post by timebent

x

ImageUploadedByStudent Room1469211652.715922.jpg

Reply 68

OP

Original post by Chittesh14

Sorry I was out.

ImageUploadedByStudent Room1469211240.697405.jpg

Original post by Chittesh14

Basically, anything which is negative and is square rooted.
It is basically, that number square rooted i.

I'll post examples wait.

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Original post by Chittesh14

Thank you Thank you Thank you so much ^-^

Reply 69

Zacken

22

Original post by Chittesh14

Uh...

\sqrt{16} = 4 \neq \pm 4i

.

Reply 70

Zacken

22

Original post by timebent

http://www.examsolutions.net/a-level-maths-papers/Edexcel/Further-Maths/Further-Maths-FP1/2013-January/paper.php#Q5
i decided to start with the left bracket.

So i tried to solve for x and see what i'd get, since the question told me there'll be 2 conjugate pairs in total i should get 1 pair from this bracket on the left.

4x^2 +9=0[br][br]4x^2=-9[br][br]x^2=-\frac{9}{4}[br][br]x=\sqrt {-\frac{9}{4}}

Your last step is wrong,

x^2 = a \iff x = \pm \sqrt{a}

so

x = \pm \frac{3}{2} i

which are indeed conjugate pairs.

Reply 71

Original post by Zacken

Uh...

\sqrt{16} = 4 \neq \pm 4i

.

You know what I meant... -16 Zacky boy.

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Reply 72

Original post by timebent

Thank you Thank you Thank you so much ^-^

Np. Try to follow what Zacken said and solve the second bracket.

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Reply 73

OP

Original post by Zacken

Your last step is wrong,

x^2 = a \iff x = \pm \sqrt{a}

so

x = \pm \frac{3}{2} i

which are indeed conjugate pairs.

oh oops i mean to put 3/2 there not the 9 and 4
thanks ^-^

Original post by Chittesh14

Np. Try to follow what Zacken said and solve the second bracket.

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yup...

Reply 74

Zacken

22

Original post by timebent

oh oops i mean to put 3/2 there not the 9 and 4
thanks ^-^

Uh, no, that wasn't the mistake... the mistake was not including the

\pm

.

Reply 75

OP

Original post by Zacken

Uh, no, that wasn't the mistake... the mistake was not including the

\pm

.

Oh ;_; when will i stop making these small mistakes

Reply 76

Original post by timebent

x

Did u manage to solve it in the end?

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Reply 77

OP