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C1 Quadratics help!

I know what to do however all the calculations i've done so far have turned out incorrect,

for A) ive done 144 - 4 (k + 1 ) (k - 4) > =0 however after expanding the brackets for (k + 1) ( k - 4 ) everything goes wrong :angry:

help please :h:

Reply 1

RDKGames

Study Forum Helper

Original post by melisss22

help please :h:

Show your expansion, please.

Reply 2

TheConfusedMedic

Maybe you're making mistakes with the signs? Eg. forgetting that - - = +?

The other common error that I can think of is that you maybe forgot that the inequality switches when you multiply/divide by -1?

eg: -a >= -3
a <= 3

(edited 7 years ago)

Reply 3

melisss22

Original post by RDKGames

Show your expansion, please.

144 - 4 ( k^2 - 4k + k - 4 )

then i did 144 - 4k ^ 2 + 16k - 4k + 16 > = 0

Reply 4

melisss22

Original post by surina16

Maybe you're making mistakes with the signs? Eg. forgetting that - - = +?

aaaaa i dont think i did ???

Reply 5

RDKGames

Study Forum Helper

Original post by melisss22

144 - 4 ( k^2 - 4k + k - 4 )

then i did 144 - 4k ^ 2 + 16k - 4k + 16 > = 0

That's good. What's wrong with it then??

Reply 6

everythingice

Original post by melisss22

144 - 4 ( k^2 - 4k + k - 4 )

then i did 144 - 4k ^ 2 + 16k - 4k + 16 > = 0

I'd recommend dividing everything by 4 outside of the brackets in the first step shown here before you do anything. It should help you get to the right solution easier. :smile: