Question

PLEASE HELP!!! I have a math test tomorrow and need help with substitution and elimination.
1) y=5x+3, y=x-9


2) 2x-y=5, -3x+4y=0

Answer 1

\(\large {
(1)\ hint
\begin{cases}
{\color{brown}{ y}}=5x+3\\
{\color{brown}{ y}}=x-9
\\ \quad \\
{\color{brown}{ y}}={\color{brown}{ y}}
\end{cases} }\)

you could do the same for the (2) one

Answer 2

or you could just solve the 1st equation of the (2) set for "y" only and substitute on the 2nd equation of (2)

Answer 3

It'd be nice if you laid out the equation so could follow through it, instead of guessing and getting it wrong

Answer 4

@jdoe0001

Answer 5

That guy jdoe0001 is good. Follow his lead @Syli

Answer 6

elimination:
move all variables to one side

y=5x+3 subtract 5x
y=x-9 subtract x so,

y-5x=3
y-x =-9 lets eliminate y bymullt. here by -1 and then add the 2 equations together so,

y-5x =3
-y+x = 9
____________
-4x = 12 divide both by -4
x=12/-4 or - 3

plug in for x and get y

y =-3-9
y=-12

do a check
-12-5(-3) =3
-12+15=3
3=3 check

here is substitution

y=5x+3
y=x-9 since y = x-9 plug in for y in eq(1)

x-9= 5x+3 add 9 both sides and subtract 5x so

-4x= 12
x=-3

we already found y and did the check

good luck on the test.

Answer 7

Thank you very much! :) @zpupster