# having trouble

#### shellann

##### New member
this is the question my son and I have gotten the same answer but the one in the back is different

Evaluate 3m3 - 2n
a) m=2 and n=3
b) m= -4 and n= -5
c) m= -1/2 and n= 3/4
d) m= 1/3 and n = -5

#### Dr.Peterson

##### Elite Member
I assume you mean 3m3 - 2n; you can use the "x2" button to make superscripts. (Or you could write 3m^3 - 2n.)

Please show us at least the answers you get (and the answers in the book), so we can see who is actually right; and for at least one of these, show your work, so we can see where you are going wrong, if at all.

I can say that the most likely errors, in my experience, would involve signs; and the second most likely would be forgetting the order of operations, that you have to cube m before you multiply it by 3.

• Harry_the_cat

#### shellann

##### New member
The answer in the back is 6

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#### Dr.Peterson

##### Elite Member
Clearly you are right and they are wrong (unless you looked at the answer to a different question).

I wonder if the person who wrote the answers misread the expression as 3m^2 - 2n . That would give 3(2^2) - 2(3) = 6 as the answer.

Are their answers for the other parts suitable for that expression, too?

In any case, you're doing fine.

#### Jomo

##### Elite Member
this is the question my son and I have gotten the same answer but the one in the back is different

Evaluate 3m3 - 2n
a) m=2 and n=3
b) m= -4 and n= -5
c) m= -1/2 and n= 3/4
d) m= 1/3 and n = -5
Were all the answers you got for all parts different from the book? Or just part a? If just part a, then next time please state that so no one spends their time on showing you all the parts.
I suspect that for part a the author used the power of 2 instead of 3 to get 6 as an answer. Good job!