C3 HW help Watch

username2250433
Badges: 13
Rep:
?
#1
Report Thread starter 2 years ago
#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
reply
tiny hobbit
Badges: 15
Rep:
?
#2
Report 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
reply
tiny hobbit
Badges: 15
Rep:
?
#3
Report 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
reply
username2250433
Badges: 13
Rep:
?
#4
Report Thread starter 2 years ago
#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
reply
MartyO
Badges: 7
Rep:
?
#5
Report 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.

g\circ f(x)=g(f(x))=g(1-2x^{ 3 })=\frac { 3 }{ 1-2x^{ 3 } } -4=\frac { 3-4(1-2x^{ 3 }) }{ 1-2x^{ 3 } }
0
reply
username2250433
Badges: 13
Rep:
?
#6
Report Thread starter 2 years ago
#6
(Original post by MartyO)
Did you get this? You'd only have to distribute and simplify.

g\circ f(x)=g(f(x))=g(1-2x^{ 3 })=\frac { 3 }{ 1-2x^{ 3 } } -4=\frac { 3-4(1-2x^{ 3 }) }{ 1-2x^{ 3 } }
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
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of East Anglia
    All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
    Wed, 30 Jan '19
  • Solent University
    Careers in maritime Undergraduate
    Sat, 2 Feb '19
  • Sheffield Hallam University
    City and Collegiate Campus Undergraduate
    Sun, 3 Feb '19

The new Gillette ad. Is it:

Man-hating bullsh*t (22)
42.31%
Pro-humanity (30)
57.69%

Watched Threads

View All