Combining like terms?

• Sep 27th 2009, 01:27 PM
dark-ryder341
Combining like terms?
This is for a physics question, but I figured since it was math-based, I might be able to post it here. The problem that I'm having is combining like terms - I know it's simple but for some reason I've forgotten.

Here's my problem:

I solved it up until here. Now I'm stuck.

C = (3.69i + 10.14j) - (-8.312i + (-4.8)j)

If only the 'i' terms can be combined with 'i' terms, and the 'j' terms only with 'j' terms, how would I do this?

Would it be 3.69i -(-8.312i) which would give me a positive answer or just 3.69i(-8.312i) where I ignore the '-' in between the two brackets (and subtract later) which would give me a negative answer?

Thanks for any help!
• Sep 27th 2009, 01:57 PM
hello
C = (3.69i + 10.14j) - (-8.312i + (-4.8)j)

=3.69i + 10.14j + 8.312i + 4.8j

=12.002i + 14.94j
• Sep 27th 2009, 02:55 PM
dark-ryder341
Alright, thanks. I was afraid of that, because I've been doing those ones wrong then...

So, for instance, if I had say:

(4.1i + (-3.75)j) - (1.30i + 2.25j)

I would get:

4.1i - 3.75j - 1.30i - 2.25j which would equal 2.8i - 6.0j?

If I wanted to square root that would it be, then, squ.rt. of (2.8)^2 + (-6.0)^2? or would it be (2.8)^2 - (6.0)^2?

Thanks again!