# C3 HW helpWatch

#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?
0
2 years ago
#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
0
2 years ago
#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
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
0
2 years ago
#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.

0
#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)
0
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