Multiplying Matrices
By Ashley
Multiplying matrices is really pretty simple. I am not really that good at math and I can figure it out so you should be able to too.
Here is a simple way my math teacher, Ms. Blackwell, told us to remember how to multiply matrices. Have you ever heard of the soda "RC Cola", well the formula is in the name. You simply multiply the rows times the columns and that will give you the answer!
There are a few rules to multiplying matrices, and here they are: 1)the inner dimensions of the two matrices must match. ex) 2x2 X 3x2 can't be multiplied but a 2x2 X 2x3 will work!
OK now lets do a simple problem: multiply [3 5] * [[5] now you simply multiply the 3
[4]]
times the 5 and you get 15 then you mult. the 5 times the 4 and you get 20 then you simply add the 15 and the 20 and the answer to your matrix is [35]!
Now a trick to see if the dimensions, at least, are right is to take the outer numbers of the dimensions and they will tell your what the dimensions of your answer should be. so the two matrices were 1x2 and 2x1 so the answer should be a 1x1 and guess what... it is!
if you have a calculator you can simply go to the matrix function and type in the numbers and hit the multiplying key and it will you the answer.
Now let's try a word problem. Say a cosmetic counter wants to see which cosmetic is their best seller. They sell lipsticks for 12.00$, blush for 9.00$, foundation for 15.00$, and eye liner for 2.00$. In a day they sell 25 lipsticks, 32 blushes, 20 foundations, and 75 eye liners. Which cosmetic gave the biggest profit.
You first put the problem into two matrices, one for the prices (row) and one for the amount sold (column). [[12.00 9.00 15.00 2.00]] x [ [25] then you just times them together! [32]
[20]
[75]]=[1038]
Did you get the right answer? If not then just try again.
www.math.toronto.edu/mathnet/plain/questionCorner/matrixmul.html this is another website that teaches how to mult. matrices.
"No act of kindness, no matter how small, is ever wasted." — Aesop, ancient Greek moralist
http://www.josephsoninstitute.org/quotes/quotecaring.htm This quote means that any time you are kind even if it seems small to you it won't be small to the person you are kind to.