Solving a system of three equations?

Question

x + y + z = 9
y + z = 7
z = 4

Please show the steps you took to solve this system of equations. Thanks for your help!!

Answer 1

This a an easy example, there are other methods but.

Substitute 4 for z every place.

x + y + 4 = 9
y + 4 = 7
4 = 4

Now remove the identity and solve the last two.

x + y + 4 = 9
y + 4 = 7

Solve one for its variable.
y + 4 = 7
Add -4 to both sides.

y = 3

Now substitute 3 into the other equation.
x + y + 4 = 9

x + 3 + 4 = 9

Combine like terms

x + 7 = 9

Add -7 to both sides.

x = 2

Answer 2

x + y + z = 9
y + z = 7
z = 4

The first thing that you do is plug z in to y + z = 7. so y + 4 = 7, so it is y = 3.

Now you plug in z and y into x + y + z = 9, x + 3 + 4 = 9, so x = 2.

Answer 3

y=7-z,
y=7-4,
y=3,
x= 9-y-z,
x=9-4-3,
x=2

Answer 4

Tonda

Stop and think about it, break it down into small steps of what you know, you know z = 4

y + z = 7 ( so substitute for z)

y + 4 = 7

y = 7 - 4 = 3

you now know "y" so substitute for y and z in the first equation

x + y + z = 9 (I'll leave it to you to perform the last step)

Answer 5

x+y+z=9
y+z=7
and z= 4

so now you know that z is 4 and the second equations says y+z=7 then subtract 4 from 7 to find out what is y now u get 3
then subtract 7 from 9 to find out what x is u get 2

z=4
y=3
x= 2
~ Kristin ♥

Answer 6

x + y + z = 9
y + z = 7
z = 4

y + z = 7
y + (4) = 7
y = 3

x + y + z = 9
x + (3) + (4) = 9
x + 7 = 9
x = 2

x = 2; y = 3; z = 4

Answer 7

y+4=7
-4 -4
y=3
x+3+4=9
x+7=9
-7 -7
x=2
(2,3,4)


Trust me on this i have a 98.7% in Algebra 2 in 8th grade and I got 100% on that test.

Answer 8

First, find y+z. Make the operation go backwards, so it would be 7-x=y. x=4 so 7-4=3. y=3.
So then, 9-4-3=x
x=7
there you go.

Answer 9

x + y + z = 9
y + z = 7
z = 4

well if z is 4 then you would do 7 minus z which equals 3
so y=3.

now 4 plus 3 equals 7 plus 2 equals nine.

z=4
y=3
x=2

Answer 10

if z = 4...
y+z=7
y+4=7 simple algebra
y=3

now we know that y=3 and z=4

x+y+z=9
x+3+4=9 another simple algebra
x=2

there you go