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OCR MEI Maths - C1 - help

How do i do 13 iii) - i don't get it :/
Screen Shot 2016-05-12 at 22.17.03.png32.9KB
write

x4 - 2 = kx2

investigate the Discriminant... this tells you how many roots the equation has.
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tmifan
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Original post by the bear
write

x4 - 2 = kx2

investigate the Discriminant... this tells you how many roots the equation has.


Discriminant = b^2 - 4ac

....Stuck. What do i do with the x^4?
Original post by tmifan
Discriminant = b^2 - 4ac

....Stuck. What do i do with the x^4?


this is a disguised quadratic...
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tmifan
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Original post by the bear
this is a disguised quadratic...


So its just:
(-k)^2 - (4 x 1 x -2)

= -k^2 + 8

Then?
Original post by tmifan
So its just:
(-k)^2 - (4 x 1 x -2)

= -k^2 + 8

Then?


discriminant = k2 + 8

what does that tell you ?
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Zacken
22
Original post by tmifan
So its just:
(-k)^2 - (4 x 1 x -2)

= -k^2 + 8

Then?


(−k)2=−k×−k=−1×k×−1×k=−1×−1×k×k=1×k×k=k2(-k)^2 = -k \times -k = -1 \times k \times -1 \times k = -1 \times -1 \times k \times k = 1 \times k \times k = k^2.
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tmifan
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Original post by the bear
discriminant = k2 + 8

what does that tell you ?


...I don't know...
(edited 7 years ago)
Reply 8
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Zacken
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Original post by tmifan
...I don't know...


What does the discriminant always being greater than 0 mean?
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tmifan
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Original post by Zacken
What does the discriminant always being greater than 0 mean?


2 roots!

but how do you know its greater than 0...from k2 + 8
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Zacken
22
Original post by tmifan
2 roots!

but how do you know its greater than 0...from k2 + 8


Well what do you know about a squared number? What do you get is you take a squared number and add a positive number?

If you cannot answer that, then think about what is (-100)^2 - what is (-200)^2 - what is (1)^2, what do they all have in common?
Reply 11
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tmifan
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Original post by Zacken
Well what do you know about a squared number? What do you get is you take a squared number and add a positive number?

If you cannot answer that, then think about what is (-100)^2 - what is (-200)^2 - what is (1)^2, what do they all have in common?


Oh duhh! sorry that was a stupid question

Okay i get it now! Thank you both!

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