Question

y = -0.4x
y = -0.8x + 2
I don't know how to do these AT ALL! Please help!!

Answer 1

how to do what?

Answer 2

well I don't know how to work this problem out

Answer 3

(systems of equations)

Answer 4

let y=y is a good start

Answer 5

ok

Answer 6

we are given that:

y = -0.4x

and

y = -0.8x + 2

so let y=y

-0.4x = -0.8x + 2, solve for x

Answer 7

so first do we add up 0.4 and -0.8?

Answer 8

essentially yes, in a more mathical way we might want to say; lets add 0.4 to each side of the equals sign

Answer 9

ok so now we have y=1.2+2?

Answer 10

not quite ....

-0.4x = -0.8x + 2
+0.4x +0.4x
----------------
0 = -0.4x + 2

Answer 11

oh ok so now we divide both sides by 2?

Answer 12

while dividing by 2 is fine ... lets assume you want to subtract by 2 instead

Answer 13

0 = -0.4x + 2
-2 - 2
--------------
-2 = -0.4x

Answer 14

if we multiply thru by 10, it may help see the problem without the decimal

-20 = -4x

Answer 15

ok but, why are we multiplying by 10?

Answer 16

because it may be helpful to see this wihtout the decimal point cluttering the issue.

-20 = -4x is mentally a simpler thing to see than -2 = -0.4x

Answer 17

oh I see so now we divide both sides by 4 and get 5 so x=5?

Answer 18

correct :)

Answer 19

ok what about solving for y?

Answer 20

well, we know x=5 ... and they gave 2 equations that define y .... so use the definition of y that you like best, and set x to 5

Answer 21

sorry I don't get that part

Answer 22

y = -0.4x ... we know the value that x has to be sooo

y = -0.4(5)

Answer 23

ok Thank you!! :)

Answer 24

youre welcome