Which is equal to 3[f(2x)] for f(x) = 3x^2+3/2?

a.15/2

b. 81/2

c. 9x^2+9/2

d.18x^2+9

Question

Which is equal to 3[f(2x)] for f(x) = 3x^2+3/2?

a.15/2

b. 81/2

c. 9x^2+9/2

d.18x^2+9

e.mccormick · Answer

What part of this is giving you trouble?

anonymous · Answer

when i try to substitute the f(x) to the  3[f(2x)] i can't get the answer

e.mccormick · Answer

You substitute 2x into f(x), then multiply through the whole thing by 3.

e.mccormick · Answer

Hmmm... and yes, if that is written right, I can see why that would not get an answer.

e.mccormick · Answer

Is it supposed to be $3[f(2)]$??  Rather than 2x?

anonymous · Answer

the answer is 108x^2 + 9/2?

anonymous · Answer

its 2x

e.mccormick · Answer

Yes, as written, $108x^2 + \cfrac{9}{2}$ would be correct.

muhammad_nauman_umair · Answer

if u want this answer then u should in question (3x)^2 instead of 3(x^2)

anonymous · Answer

well there was another option to solve this problem : if the correct answer is not in the given choices, write you answer

e.mccormick · Answer

Ah, yes...  I see what Muhammad_Nauman_Umair is pointing out.

anonymous · Answer

thanks for your help guys @Muhammad_Nauman_Umair  and @e.mccormick

e.mccormick · Answer

$(2x)^2=4x^2$
$3\times 4x^2=12x^2$
$3\times 12x^2=36x^2$

Which is what I got the first time... and when you said 108 I thought I had forgotten to multiply by 3.

e.mccormick · Answer

$36x^2 + \cfrac{9}{2}$ is what it should be.

muhammad_nauman_umair · Answer

36x^2+9/2