Question

Find -3A+6B
A=[-3 5 -6] B=[-2 6 7]
[9 -5 3] [2 -1 -6]

Answer 1

\[\mathbf A=\begin{bmatrix}-3&5&-6\\9&-5&3\end{bmatrix}\]
\[\mathbf B=\begin{bmatrix}-2&6&7\\2&-1&-6\end{bmatrix}\]

\[-3\mathbf A=\begin{bmatrix}-3\times-3&-3\times5&-3\times-6\\-3\times9&-3\times-5&-3\times3\end{bmatrix}\]
\[6\mathbf B=\begin{bmatrix}6\times-2&6\times6&6\times7\\6\times2&6\times-1&6\times-6\end{bmatrix}\]

Answer 2

@UnkleRhaukus shouldn't all of the 3's be negative?

Answer 3

yeah i fixed that now*

Answer 4

@UnkleRhaukus oh ok. so do i just multiply them then subtract?

Answer 5

yeah,


the element on the top left will be

(−3×−3)+(6×-2)

Answer 6

@UnkleRhaukus 15x-2?

Answer 7

how did you get that?

Answer 8

no 3x-5..?

Answer 9

@UnkleRhaukus i'm so confused.

Answer 10

ok, lets go slower
what does this simplify to become?
\[-3\mathbf A=\begin{bmatrix}-3\times-3&-3\times5&-3\times-6\\-3\times9&-3\times-5&-3\times3\end{bmatrix}\]

Answer 11

9 -15 18
-27 15 -9 @UnkleRhaukus

Answer 12

good

Answer 13

and what about

\[6\mathbf B=\begin{bmatrix}6\times-2&6\times6&6\times7\\6\times2&6\times-1&6\times-6\end{bmatrix}\]

Answer 14

-12 36 42
12 -6 -36 @UnkleRhaukus

Answer 15

i got -3 21 60
-15 9 -45 as my answer @UnkleRhaukus

Answer 16

right so you have


-3A + 6B

= [ 9 -15 18 ] [ -12 36 42 ]
[ -27 15 -9 ] + [ 12 -6 -36 ]


= [ 9-12 -15+36 18+42 ]
[-27+12 15-6 -9+-36 ]

Answer 17

that's right!

Answer 18

thanks for your help :) @UnkleRhaukus