Peform the following matrix multiplicattions without using a calculator

[18 -4]
[6 -1] X [2]
[1/2 2] [3]

Question

Peform the following matrix multiplicattions without using a calculator

[18 -4]
[6    -1] X [2]
[1/2  2]    [3]

anonymous · Answer

Do you know how to do matrix multiplication?

geometry_hater · Answer

No how do i multiply 18 times 2 ?

anonymous · Answer

Since you are multiplying a 3x2 matrix by a 2x1 matrix the resultant matrix will be 3x1. To multiply you take element of the first row and multiply it by the corresponding element in the first column (of the other matrix). Then repeat his. This gives you $$[18*2+(-4)*3]$$$$[6*2+(-1)*3]$$$$[(1/2)*2+2*3]$$
Which gives
$$[24]$$
$$[9]$$
$$[7]$$

anonymous · Answer

You can learn more here: http://www.khanacademy.org/video/matrix-multiplication--part-1?playlist=Linear%20Algebra

geometry_hater · Answer

ahh ha!!..... i get it now

anonymous · Answer

I forgot these types of problems, but don't you use something like the distributive prop?