Question

pls pls help me... medal
Use the substitution method to solve the following system of equations.

3x + y – z = 2
2x + y + 2z = 8
2x – 3y + z = 21

Answer 1

hi

Answer 2

Can you help me with the question pls

Answer 3

If you look at the first equation, you could rewrite that as z = 3x + y -2.
Use this to replace z in the other two equations and simplify.
What do you get?

Answer 4

but why isolating the z though @ZeHanz

Answer 5

Doesn't matter which one you isolate. I just took z because it was in the first equation and I didn't have to divide to isolate it.
If you isolate another, you'd do the same: replace in the two other equations.

Answer 6

trust me, i tried but i couldn't get the solution. they didn't make any sense @ZeHanz

Answer 7

@ZeHanz pls help me

Answer 8

OK, let's see what we get with z = 3x + y -2 in eqations 2 and 3:

2x + y + 2(3x + y -2) = 8
2x – 3y + 3x + y -2 = 21

We only have x and y in these equations.
Simplified:

2x+y+6x+2y-4=8
2x-3y+3x+y-2=21

8x+3y=12
5x-2y=23

Answer 9

Now we can again use substitution, although this time, things are not so nice:
Suppose we isolate y from the first one: 3y=12-8x, so y=4-8x/3
Suppose we isolate x from the first one: 8x=12-3y, so x=12/8-3y/8, even worse...

I would uese elimination from this point (after all, we already DID use substitution):

8x+3y=12 multiply with 2 : 16x+6y=24
5x-2y=23 multiply with 3: 15x-6y=69

Add:

16x+6y=24
15x-6y=69
---------- +
31x =93

So x=93/31=3

Now we can first find y, then z.