#Need help, need to know for exam tomorrow

62 messages · Page 1 of 1 (latest)

subtle sedge
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@coral cedar I’m not sitting further but don’t u just factorise the function to get (2x + 1)?

dull robin
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im pretty sure you just sub x=-1/2 into the equation

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so it equals zero

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but dont quote me on that

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@coral cedar

subtle sedge
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Or maybe not I might be dumb,

dull robin
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same here but i think i could be right

subtle sedge
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Why sub -1/2 @dull robin ?

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Where does that number come from tf

dull robin
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(2x+1)

subtle sedge
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Thank god I’m not taking further

dull robin
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x=-1/2

subtle sedge
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Ohhhh

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Negative reciprocal?

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Makes sense

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Ahh ty

dull robin
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well thats what i think anyway

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but im fairly confident its right

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yeah im right, just checked

barren tundra
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Lol I just did this q

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Do u need help with b) as well

coral cedar
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@dull robin

barren tundra
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2x+1=0
So x =-1/2

coral cedar
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ohhh got you

dull robin
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yeah

coral cedar
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thank you

dull robin
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what he said

barren tundra
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In general if (x-a) is factor then f(a) = 0

dull robin
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watch this

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if you still dont understand

barren tundra
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And if it’s (ax+b) then f(-b/a)

coral cedar
barren tundra
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We can see straight away that a must be 100 and c = -9

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So (2x+1)(100x²+bx-9)
To find b we can compare the coefficients of the x² terms when expanding
So it would be 1(100x²) + 2bx² = 100x²
Therefore b = 0 so the quadratic factor is (100x²-9) which factorises to (10x±9)

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a) Let 2x+1 =0 solve for x and sub into equation should end up with a answer of 0

b) let equation equate to 0 and factorise, to factorise use algebraic division as you know 2x+1 Is a factor divide it by f(x) should end up with quadratic which you can factorise a bit easier, once done you should get 3 values max for x

coral cedar
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tysm

coral cedar
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@barren tundra @barren tundra the mark scheme shows three solutions (-0.3, 0.3 and -0.5) but I dont understand how you can get -0.5

barren tundra
coral cedar
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(10x-3)(10x+3)

coral cedar
barren tundra
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your meant to have another factor

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another bracket

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it should be (10x-3)(10x+3)(2x+1)

coral cedar
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how does 100x^2-9 factorise into three brackets though

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that would make it a cubic

barren tundra
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the highest polynomial is 3

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so 3 factors

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200x^3

coral cedar
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right got you

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so what did i do wrong

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i divided f(x) by (2x+1) to get the quadratic and then factorised if

barren tundra
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you know how to facotrise a quadratic too right

coral cedar
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yes

barren tundra
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so what did you get when you did that

coral cedar
barren tundra
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yes and then you put the (2x+1) next to it as well

coral cedar
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ohhhh

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thank you

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that’s what i wasn’t getting