solve using row reduction:

4x+9y=1
3x+7y=1

Question

solve using row reduction:

4x+9y=1
3x+7y=1

.sam. · Answer

row reduction=elimination?

anonymous · Answer

im not exactly sure what you mean

anonymous · Answer

im trying to find x and y

.sam. · Answer

http://en.wikibooks.org/wiki/Linear_Algebra/Row_Reduction_and_Echelon_Forms

anonymous · Answer

@.Sam. ,you are right

.sam. · Answer

First make x the same
4x+9y=1     times 3
3x+7y=1     times 4
-------------------------------------
12x+27y=3
12x+28y=4
========
          -y=-1
            y=1

4x+9y=1
4x+9(1)=1
4x+9=1
Solve for x

anonymous · Answer

x=1
y=-1?

jim_thompson5910 · Answer

well row reduction deals with matrices and elimination deals with systems of equations, so they're slightly different, but they get you the same answer.

anonymous · Answer

i need to solve it using the matrix

anonymous · Answer

see here @m23chris : http://www.math.hmc.edu/calculus/tutorials/linearsystems/

anonymous · Answer

we never really did it like this its hard to understand

jim_thompson5910 · Answer

4x+9y=1 
3x+7y=1



4        9          1
3        7          1



1        9/4          1/4               (1/4)*R1
3        7          1



1        9/4          1/4
0        1/4          1/4                   R2 - 3*R1 ---> R2



1        9/4          1/4
0          1               1                  4*R2



1          0              -2                 R1 - (9/4)*R2 ---> R1
0          1               1               



So the solutions are x = -2 and y = 1

anonymous · Answer

so youre dividing by 4 in the first row

jim_thompson5910 · Answer

yes in the third step

anonymous · Answer

ok i get it now but i have 2 more questions involving 3 rows using the matrix can you help me?

jim_thompson5910 · Answer

sure, just make a new question and let me know about it

anonymous · Answer

ok