I need help with multiplying matrices please?

Question

anonymous · Answer

|dw:1368729304355:dw|

anonymous · Answer

I know the dimensions of the product of HJ will be 2 x 1, but I'm not quite sure how to get the actual matrix of the product.

amistre64 · Answer

rotate J 90 degrees so that the top value is at the left side

anonymous · Answer

Rotate 90 degrees

amistre64 · Answer

then place it over the matrix and multiply down the columns


-1   3    7
---------
  2   5   10
-4   3   -6


  2(-1)   5(3)   10(7)
-4 (-1)  3(3)   -6(7)

and add across the rows

amistre64 · Answer

2(-1)   5(3)   10(7)
-4 (-1)  3(3)   -6(7)


 -2  +15  +70 = b1
  4    +9    -42 = b2

anonymous · Answer

Oh, okay! So then it would be
 83
-29
right?

amistre64 · Answer

as long as you added correctly, sure :)

anonymous · Answer

I think I added correctly.. lol hopefully. Anyway, thank you!

amistre64 · Answer

good luck

amistre64 · Answer

when they give you J as a bunch of column vectors, the process is the same, just do it for each column vector individually