Question 820632
Use substitution to solve each system of equations. If the system does not have exactly one solution, state whether is has no solution or infinitely many.
18. 2x-y=-4
-3x+y=-9
--------------
Solve either equation for 1 of the variables, either x or y.
2x-y=-4 =
y = 2x+4
---
Sub for y in the other equation
-3x+y=-9
-3x+ (2x+4) = -9
-x + 4 = -9
x = 13
---
Sub for x in any eqn to find y.
y = 2x+4
y = 2*13 + 4
y = 30
===================
That's all.
----------------
20. 2x+3y=1
-3x+y=15
Solve for the one that's most convenient - y in the 2nd equation.
------
22. 5r-s=5
-4r+5s=17
Same as above
24. x-3y=0
3x+y=7 
26. 0.5x-2y=17
2x+y=104 
28. x=1/2y+3
2x-y=6