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Simultaneous Equations help!

2771024

How would I solve this?

4x + y = 25
x - 3y = 16

None of the coefficients are the same so I dont know what to do?

Reply 1

username963570

Original post by JackT2000

How would I solve this?

4x + y = 25
x - 3y = 16

None of the coefficients are the same so I dont know what to do?

Change one of the equations to make one of the coefficients the same, and solve from there.*

Reply 2

B_9710

Multiply one of the equations by a number to make one of the coefficients the same.

Reply 3

Scary

rearrange one of them for y then substitute that in the other, to get a value for x, then substitute that value into one of the equations to get y

Reply 4

Zacken

In this case:

y = 25 - 4x

then sub this into the second equation and solve for

x

Reply 5

Kendrik Lamar

Original post by JackT2000

How would I solve this?
4x + y = 25
x - 3y = 16

Step 1:Make y the subject in both equations-
First equation becomes:
y=25-4x
Second equation becomes
-3y=16-x
3y=-16+x
3y=x-16
y=(x-16)/3
Step 2
Equate the two equations and solve for x
If y=25-4x and y also equals (x-16)/3
Then 25-4x=(x-16)/3
25-4x=(x-16)/3
3(25-4x)=x-16
75-12x=x-16
Or x-16=75-12x
x=75-12x+16
x=91-12x
x+12x=91
13x=91
x=91/13
x=7
Step 3:
Use the solution for x to solve for y
4x+y =25
But x=7
So4(7)+y=25
28+y=25
y=25-28
y=(-)3
Answers:
x=7,
y=(-)3

(edited 7 years ago)

Reply 6

math42

Original post by JackT2000

How would I solve this?

4x + y = 25
x - 3y = 16

None of the coefficients are the same so I dont know what to do?

quickest way is just multiply the second equation by 4 then subtract equations

Reply 7

RDKGames

Study Forum Helper

Original post by 1 8 13 20 42

quickest way is just multiply the second equation by 4 then subtract equations

I think multiplying the first by 3 and adding them would be faster than that :tongue:

Reply 8

math42

Original post by RDKGames

I think multiplying the first by 3 and adding them would be faster than that :tongue:

I would prefer mine as I only have to do 39/13, instant, 91/13 one might think for half a second..then again I suppose there are more negatives to contend with
In any case, the important thing is multiplying is faster than subbing for y