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If f(x)=3x+6,g(x)=4x+k and fog(x)=gof(x)...

If `f(x)=3x+6,g(x)=4x+k and fog(x)=gof(x)` then k= . .

A

`-9`

B

18

C

`1//9`

D

`9`

Text Solution

Verified by Experts

The correct Answer is:
D
We have,
`f(x)=3x+6,g(x)=4x+k`
Since, `fog(x)=gof(x)`
`impliesf(g)(x)=g(f(x))`
`impliesf(4x+k)=g(3x+6)`
`implies3(4k+k)+6=4(3x+6)+k`
`implies3k-k=24-6`
`implies2k=18impliesk=9`
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MHTCET PREVIOUS YEAR PAPERS AND PRACTICE PAPERS-SOLVED PAPER 2019-MCQS
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