3x-7y=21. Need the 3 ordered pairs where #1: x=0, is __ #2: y=0, is __ #3: y=-6, is __.

- anonymous

3x-7y=21. Need the 3 ordered pairs where #1: x=0, is __ #2: y=0, is __ #3: y=-6, is __.

- schrodinger

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- anonymous

ok, so for the first one, you would plug in 0( which is x) in the equation.:
3(0)-7y=21
0-7y=21
y=21/-7
y=-3, so first ordered pair would be (0, -7)
for the second one you would plug in0 for y this time, and in the third one you would plug in -6 for why, and solve for x on that too. then you have your three ordered pairs

- anonymous

I am still not getting it so need more help

- anonymous

ok, so lets do the second one

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## More answers

- anonymous

ok i tried but got lost

- anonymous

the second one says y= 0
so we are going to plug in 0 for the y, in the function:
3x-7y=21
so when we plug in 0 for y, the function now says:
3x-7(0)=21
next we multiply 0 times 7, so we get:
3x-0=21, which is basically
3x=21
next, we finaly divide 3 on both sides to get x by itself
x=21/3 which is x =7

- anonymous

so now that we know that x=7 , when y=0, the ordered pair is in the form of (x,y) which in this case, it would be (7, 0). that is your second set of points. did you understand this?

- anonymous

well when i did it it was a little different but it did not look right but had the same answer

- anonymous

for the last one i started with 3x-7(-6)=21

- anonymous

then i had 3x-42=21

- anonymous

ok wait a sec

- anonymous

whats -7 *-6?

- anonymous

don't I replace the y with -6?

- anonymous

yes, but what is -7 times -6. can you hold up for a sec

- anonymous

sure

- anonymous

3x-7(-6)=21 is the correct next step, but what do you get when you multiply negative 7 times negative 6?

- anonymous

you get positive 42

- anonymous

so you should have 3x-42=21

- anonymous

no, its going to be
3x+42=21 because we got positive 42, not negative 42

- anonymous

ok i see

- anonymous

yes
3x+42=21, what do we do next?

- anonymous

get x by itself by using 3

- anonymous

OK WAIT

- anonymous

we still have that 42 there, and we need to get rid of it,
so how do we get rid of that 42:
3x+42=21

- anonymous

3x +42 -42 = 21 +42 - 42

- anonymous

there we go! and what do we get?

- anonymous

3x=21

- anonymous

wait whats 21-42? -21!

- anonymous

huh?

- anonymous

I thought the 42s cancelled each other out

- anonymous

yes, but its not 3x=21 its 3x=-21

- anonymous

ok I don't get it

- anonymous

so this is what you got
3x +42 -42 = 21 +42 - 42

- anonymous

right

- anonymous

why did you add 42 both sides? you were only supposed to subtract 42 on both sides. try it again,

- anonymous

3x +42 -42 = 21- 42 is what you should get

- anonymous

ok i put an extra one in there

- anonymous

exactly so figure it from this:
3x +42 -42 = 21- 42

- anonymous

ok so 3x +42 -42 = 0

- anonymous

21 -42= -21

- anonymous

yes so it should be
3x=-21

- anonymous

so (-21,-6) is the ordered pair

- anonymous

we stil need to find x! we were left with
3x=-21 !
remember we need to get x by itself!

- anonymous

ok so we us 3 on both sides

- anonymous

we divide 3 by both sides

- anonymous

damn this thing hangs up on me a lot. so we should end up with x = 21

- anonymous

whats -21/3?

- anonymous

-7

- anonymous

so x=-7.
gosh, what grade are you in? and math level?

- anonymous

I just started college last year Oct and I graduated in 1969 and had just basic math. I was able to transfer 52 credits from my military career. So I am about a late sophmore or early junior. math is 092 which is pre algebra

- anonymous

college 0.0i learned this in 6th and 7th.

- anonymous

ya I know but I have never had algebra before

- anonymous

and im in 9th. yaaay! i feel so smart!

- anonymous

when i was in high school we did not have algebra and geometry. it did not exist

- anonymous

so when i was in 12th they were just starting it as an elective.

- anonymous

I guess that is why it is so hard for me.

- anonymous

whoa! it really does amaze me how far human intelligence has gone. I cant imagine how advanced our human race will be in he next 40 years

- anonymous

ya i know. i wish there was a way for me to shock the heck out my brain so it would be easier for me to learn

- anonymous

lol, so do i! agh sooo much work!

- anonymous

ya but you understand this. I son't understand any of it. I just started in Jan to learn this junk

- anonymous

ya, this si easy. but im doing precal, and ap microecon, and ap Human Geogarohy, and ap bio

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