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# C3 HW help

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1. Im stuck on this question:

Show that the composite function gf is (8x^3 - 1) / (1 - 2x^3)

f(x)= 1 - 2x^3
g(x)=(3/x) - 4

I subbed f into g but didnt get it
any help appreciated

also, solve gf(x)=0, if i set it = 0 then i cant bring anything across, do i have to factorise and cancel down the bottom maybe?
2. (Original post by not_lucas1)
Im stuck on this question:

Show that the composite function gf is (8x^3 - 1) / (1 - 2x^3)

f(x)= 1 - 2x^3
g(x)=(3/x) - 4

I subbed f into g but didnt get it
any help appreciated

also, solve gf(x)=0, if i set it = 0 then i cant bring anything across, do i have to factorise and cancel down the bottom maybe?
You need to put 1-2x^3 where the x is in g(x) and then put it all over the same denominator
3. (Original post by not_lucas1)
Im stuck on this question:

Show that the composite function gf is (8x^3 - 1) / (1 - 2x^3)

also, solve gf(x)=0, if i set it = 0 then i cant bring anything across, do i have to factorise and cancel down the bottom maybe?
0 times anything is 0 so when you multiply up by the denominator you just get the numerator =0
4. (Original post by tiny hobbit)
You need to put 1-2x^3 where the x is in g(x) and then put it all over the same denominator
i did and i didnt get the same answer
5. (Original post by not_lucas1)
i did and i didnt get the same answer
Did you get this? You'd only have to distribute and simplify.

6. (Original post by MartyO)
Did you get this? You'd only have to distribute and simplify.

No but I think you're correct. I didnt think to put 4/1 and then make it a common denominator (i think that is what you have done anyway)

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