algebra
posted by Algebra PLEASE HELP!! on .
Explain why the addition method might be preformed over the substitution method for solving the system
2x – 3y = 10
5x + 2y = 6
What is the solution of this system?

2 x – 3 y = 10 Multiply both sides by 2
4 x  6 y = 20
5 x + 2 y = 6 Multiply both sides by 3
15 x + 6 y = 18
4 x  6 y = 20
+
15 x + 6 y = 18

4 x + 15 x  6 y + 6 y = 20 + 18
19 x = 38 Divide both sides by 19
x = 38 / 19
x = 2
To get the value of y you need to use the substitution method.
Substitute x = 2
into equation
2 x  3 y = 10
2 * 2  3 y = 10
4  3 y = 10
 3 y = 10  4
 3 y = 6 Divide both sides by  3
y = 6 /  3
y =  2 
The point of intersection of the graphs of the equations of the system
Ax – 4y = 9
4x + By = –1
is (–1, –3). Explain how to find the values of A and B, then find these values. 
(1 , 3) = ( x,y)
put the X and Y values into the first equation,
Ax4y=9
A(1) 4(3)= 9
A + 12=9
A=3
A= 3 [ Multiply by (1)]
Now put the X and Y values to the second equation,
4( 1) +B( 3) =1
4 3B=1
3B= 3
B=1 [ Multiply by negative (1)]
Just check are those ans is right, put the all values to the equation......
3(1)4(3)=9
9=9
And, 4(1)+(1)(3)=1
4 + 3=1
1 = 1
So, (A,B)= ( 3, 1 )