## bless 2 years ago 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

1. e.mccormick

What part of this is giving you trouble?

2. bless

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

3. e.mccormick

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

4. e.mccormick

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

5. e.mccormick

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

6. bless

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

7. bless

its 2x

8. e.mccormick

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

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

10. bless

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

11. e.mccormick

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

12. bless

13. e.mccormick

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

14. e.mccormick

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