2 math substitution?

Question

1) 3x+y=3
9x-y=-11


2) x-2y=10
3x+10y=14

Answer 1

1)
first, you have to solve one of the equations for the variable, it doesn't matter which one.

y=-3x+3

now, take the second equation and substitute the first one in.

since y equals -3x+3, you can just put that in the equation instead of y, giving you one variable.

9x- (-3x+3) =-11

since you are subtracting, the y value, it's a good idea to change the signs so you don't get confused....

9x + 3x -3 =-11

now you just solve.

12x-3=-11

12x=-8
x=-8/12
x=-2/3

now, plug the x value back into one of the original equations, it doesn't matter which one.

3(-2/3) +y=3

the 3s cancel out, you get -2+y=3
y=5

now just check the equation.. i like to check it in the other equation just to make sure.

9(2/3) -5 = -11

6 -5=-11

-11=-11

x= -2/3
y=5

2. i don't like doing people's hw for them, try to do this one by yourself.

Answer 2

1) y= 11+ 9x, so plug it in now: 3x + 11 + 9x = 3, 12x+11=3, 12x = -8, x= -2/3, plug x in now to get y: y=-5

2) x= 10+2y, plug in: 3(10+2y) + 10y = 14, 30 + 6y +10y = 14,
30+16y=14, 16y = -16, y= -1, plug in y to get x: x= 12

need any more help on stuff like this hit me up, good luck

Answer 3

1)

your goal is to get one equasion to
y=

3x +y = 3 |-3x
y = 3- 3x
now you substitute the y in the second equasion

9x-(3-3x)= -11
9x-3 +3x= -11 | +3
9x+3x=-11 +3
12x = -8 | /12
x= -2/3

and now you just put in x to get y

y=3-3x
y= 3-3(-2/3)
y= 3 +(6/3)
y=3+2
y=5

Answer 4

3x+y=3
9x-y=-11

y=3-3x
9x-3x+3=-11
6x+3=-11
6x=-14
x=-14/6=-2 2/6=-2 1/3- =-7/3

3/1*-7/3+y=3
-7+y=3
y=10

x-2y=10
3x+10y=14
x=10+2y
3(10+2y)=14
30+6y=14
6y=-16
y=-2 4/6= -2 2/3= -8/3

x-2/1(-8/3)=10
x-16/3=30/3
x=46/3

Answer 5

substitution is quite simple once you get the hang of it.
first, solve for one variable
9X-Y=-11
9X+11-Y=0
9X+11=Y
ok. good, we now know what y equals.
now, substitute this in for y in the other equation! substitution!
so,
3X+(9X+11)=3
12X+11=3
12X=-8
X=-8/12
reduce to -2/3
so, now we know what X equals.
put -2/3 back in the equation in place of X
3(-2/3)+Y=3
-2+Y=3
Y=5
so, answers are X= -2/3 and Y=5