MATH 240 Lecture Notes - Lecture 4: Main Diagonal, Identity Matrix
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With regular multiplication of say 6*7, you can just add 7 to itself 6 times. You can multiply two matrices together only if the first matrix has the same number of columns as the second has rows. Also, the size of the matrix can change. (cid:888) (cid:887)] [(cid:884) (cid:885) (cid:886) (cid:882) (cid:890) (cid:891) (cid:885)] Ok, the first thing to check is if the two matrices can actually be multiplied. The first is a (cid:884) (cid:884) and the second is a (cid:884) (cid:885) so we can multiply them. We need to multiply the first row of the first matrix by the first column of the second matrix. So the first entry in our matrix is a 4. Next, we want to compute the first row, second column entry of our matrix. So we multiply the first row of our first matrix by the second column of our second matrix. (cid:884)(cid:4666)(cid:884)(cid:4667)+(cid:882)(cid:4666)(cid:890)(cid:4667)=(cid:886) (cid:884)(cid:4666)(cid:885)(cid:4667)+(cid:882)(cid:4666)(cid:891)(cid:4667)=(cid:888) (cid:888)(cid:4666)(cid:884)(cid:4667)+ (cid:887)(cid:4666)(cid:890)(cid:4667)= (cid:884)(cid:890)