SOLUTION: {{{(3a-12b+c)-(6a+20b-3c)}}} i can not understand what i am doin wrong in this prob.. i took the paren. away..{{{3a-12b+c-6a+20b-3c}}} then i multiplied everything in the secon

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: {{{(3a-12b+c)-(6a+20b-3c)}}} i can not understand what i am doin wrong in this prob.. i took the paren. away..{{{3a-12b+c-6a+20b-3c}}} then i multiplied everything in the secon       Log On


   

Question 14393: %283a-12b%2Bc%29-%286a%2B20b-3c%29
i can not understand what i am doin wrong in this prob..
i took the paren. away..3a-12b%2Bc-6a%2B20b-3c
then i multiplied everything in the secon par. by 1 and changed the signs...
3a-12b%2Bc-6a-20b%2B3c
then i combined like terms...
i got the answer
3a-8b%2B4c
now i know that it was wrong cause my teacher told me that it was...but can you please help me to beter under stand this?
thanks
Answer by elima(1433) About Me  (Show Source):
You can put this solution on YOUR website!
%283a-12b%2Bc%29-%286a%2B20b-3c%29
3a-12b%2Bc-6a-20b%2B3c
3a-8b%2B4c
Why did you subtract the -12b and the -20b?
You need to remember they are both negative numbers, so you will actually add them and keep the negative sign.
=)