Thread: Can anyone explain subsitiution to me please?

I am really not understanding the substitution method. Can someone please explain it to me?

Example:

Y=4x-9
y= x-3

I would really appreciate it =]

Hello Lexifer.

Originally Posted by Lexifer

I am really not understanding the substitution method. Can someone please explain it to me?

Example:

Y=4x-9
y= x-3

I would really appreciate it =]

You have to equations
Y=4x-9 (eq1)
y= x-3 (eq2)

You know y because of (eq2) and so you substitute it in (eq1), this leads to

x-3 = 4x-9 (eq2 in eq1)

and you solve it for x.

Back to the two equations
Y=4x-9 (eq1)
y= x-3 (eq2)

You can use a substitution for x, too.
solving (eq2) for x

x = y+3 (eq2' )

and substitute it in (eq1) for x

4(y+3)-9=y (eq2 in eq1)

[In (eq1) you write y+3 instead of x because of eq2' ]

now you need to solve this equation for y

Still any questions? Then let us know

Yours
Rapha