rootbeer003:
help
satellite73:
...
satellite73:
add means add i can't write it here, but it is clear right? add one to the other
satellite73:
\[ M= \left[ {\begin{array}{cc} 31 & 24 &42 \\ 64 & 17& 35 \\ \end{array} } \right] \]
satellite73:
figured out how to write it! check my arihmetic
satellite73:
is it right?
satellite73:
looks reasonable
satellite73:
\[a_{12}=17\] it is the total number of medium zipper sweaters
satellite73:
if you add all the elements of row two, you get the total number of sweaters with zippers
satellite73:
the store has 77 large sweaters, that is what you get when you add up column 2
rootbeer003:
keep goen
satellite73:
that is all
satellite73:
oh except for the last one, which you get by subtracting instead of adding i will let you do that for yourself i added, you can subtract
satellite73:
all good except the last one you subtracted girls from boys, it should be boys from girls just change the sign of each entry
satellite73:
ok good
satellite73:
do you know how to multiply two matrices?
rootbeer003:
no
satellite73:
i was afraid of that it is not that hard in this case you will get only a one by four matrix see if you can see this http://www.wolframalpha.com/widgets/view.jsp?id=7edcfb2d8f6a659ef4cd1e6c9b6d7079
satellite73:
satellite73:
second one is the answer
rootbeer003:
hey it wont let me see pictures, lets go on peeranswers
satellite73:
i'll just write it
rootbeer003:
ok
satellite73:
\[[560,1116,1388,1096]\]
satellite73:
b you get by subtracting \[1388-1116=272\]
satellite73:
you want to know where those numbers come from?
rootbeer003:
yes i need steps
satellite73:
to multiply you have a one by two matrix times 2 by four matrix the result will be one by four
satellite73:
you need four numbers in other words for the first entry it will be \[22\times 5+18\times 25=560\]
satellite73:
second entry \[22\times 18+18\times 40=1116\]
satellite73:
third entry \[22\times 32+18\times 38=1388\]
satellite73:
fourth entry \[22\times 40+18\times 12=1096\]
rootbeer003:
any more steps?
satellite73:
no that is it write those numbers in a row like i did above
satellite73:
okey dokey
satellite73:
damn really? you have to use cramers rule and show your work so you can't cheat?
rootbeer003:
whats is cramers rule
satellite73:
you need to solve for x and y you are going to need the determinate of the matrix taken from the coefficents, \[
satellite73:
\[\left[ {\begin{array}{cc} 4 & 3 \\ -3 & -1 \\ \end{array} } \right]\]
satellite73:
that determinant is \[4\times (-1)+3\times (-3)=-13\]
satellite73:
that number will be your denominator to find x, replace the x values on the matrix by the number on the right and find the determinate of the matrix
satellite73:
\[\left[ {\begin{array}{cc} 4 & 3 \\ 7 & -1 \\ \end{array} } \right]\]
satellite73:
that determinate is \[4\times (-1)+3\times 7=17\] that makes \[x=\frac{17}{-13}\]
satellite73:
let me check that this is right
satellite73:
nope i screwed up somewhere have to start again
rootbeer003:
the whole thing
satellite73:
give me a minute
satellite73:
yeah it would help if i did it right, so lets start again with this matrix
satellite73:
\[\left[ {\begin{array}{cc} 4 & 3 \\ -3 & -1 \\ \end{array} } \right]\]
satellite73:
the determinate is
satellite73:
\[4\times (-1)-3\times (-3)=5\]
satellite73:
then this one \[\left[ {\begin{array}{cc} 4 & 3 \\ 7 & -1 \\ \end{array} } \right]\]
satellite73:
the deterinant is \[
satellite73:
\[4\times (-1)-3\times 7=-25 \]
satellite73:
so \[x=\frac{-25}{5}=-5\]
satellite73:
now we can use cramers rule to solve for y, but it is not necessary since \[4x+3y=4\]and we know \[x=-5\] we can solve \[5(-5)+3y=7\\ -20+3y=4\\ 3y=24\\ y=8\]
satellite73:
good enuf for me if you want a clear easy explanation of cramers rule look here http://www.coolmath.com/algebra/14-determinants-cramers-rule/01-determinants-cramers-rule-2x2-02
satellite73:
oh btw the answer is \((-5,8)\) or \[x=-5,y=8\]
rootbeer003:
do i put that
satellite73:
at the end maybe
satellite73:
btw you did not find y using cramers rule, just x so maybe they will be annoyed, i don't know
rootbeer003:
o well
rootbeer003:
new thread..
satellite73:
kk
Eiwoh2:
lol so long XD
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