Solving Systems of Equations by Substitution.
1.
-3x + 3y = 4
-x + y = 3
2.
-5x - 8y = 17
2x - 7y = -17

- calculusxy

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- calculusxy

@jim_thompson5910 @Nnesha

- calculusxy

@mathstudent55

- calculusxy

This is my work for question 1.
we could figure out the value of y by:
y = 3 + x
-3x + 3(3 + x) = 4
is that correct?

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## More answers

- calculusxy

i need to solve for x, which i know, but i just wanted to know whether my set up was fine or not.

- Nnesha

yep yep right :=)

- calculusxy

so then we can simply it to:
-3x + 9 + 3x = 4

- Nnesha

yep

- calculusxy

but if we do -3x + 3x = 0x and I am not even sure if there is any such thing as 0x.

- Nnesha

yes so they cancel out

- Nnesha

thats mean no solution both sides are not equal
\[9 \cancel =4\]

- calculusxy

oh okay :)

- calculusxy

and for the next one...

- Nnesha

yep

- calculusxy

we can figure out the value of x...
2x - 7y = -17
2x = -17 + 7y
2x / 2 = (-17 + 7x) / 2
x = -8.5 + 3.5x

- Nnesha

hmm you mean
x = -8.5 +3.5 y right ?

- calculusxy

yes sorry :)

- Nnesha

its okay yep right

- calculusxy

-5(-8.5 + 3.5y) - 8y = 17

- calculusxy

42.5 - 17.5y - 8y = 17
42.5 - 25.5y = 17
-25.5 - 25.5y = 17
-25.5y = 42.5
y = 1.67
i am pretty sure i am wrong it's going on decimals.

- Nnesha

well i don't understand the 3rd line

- calculusxy

if i did 17 - 42.5 = -25.5

- Nnesha

yep that's right you need to move 42.5 to the right side then you will get Perfect one

- calculusxy

what do you mean by moving 42.5?

- Nnesha

i meant you have to subtract 42.5 both sides :=)

- Jacob902

correct

- calculusxy

so what i did was correct right?

- Nnesha

\(\color{blue}{\text{Originally Posted by}}\) @calculusxy
42.5 - 17.5y - 8y = 17
42.5 - 25.5y = 17
-25.5 - 25.5y = 17
-25.5y = 42.5
y = 1.67
i am pretty sure i am wrong it's going on decimals.
\(\color{blue}{\text{End of Quote}}\)
well here 3rd line you need to subtract 42.5 both sides
i don't why there is -25.5 -25.5y

- calculusxy

oh yeah

- calculusxy

my mistake :\

- Nnesha

:=) doing gREAT

- calculusxy

y = 1 right?

- Nnesha

yep right!

- calculusxy

and then we would do:
-5x - 8(1) = 17
-5x - 8 = 17
-5x = 25
x = -5

- Nnesha

gO_OD to go!

- calculusxy

thanks :) I have another question. it's small and related to basic physics. can u help?

- Nnesha

PHYSICS hmmmm not sure

- calculusxy

can u just see it? if u can't do it then u don't have to.

- Nnesha

ye sure!

- calculusxy

okay. here it is...

- calculusxy

If i'm driving in a car at 30kph and a friend is driving in a car with the same mass at 60kph, my friend's car's kinetic energy is bigger than mine by a factor of what? (that is, divide my friend's over mine.)

- Nnesha

i'm not sure havn't done physics n a while sorry

- calculusxy

okay thank you though :)

- Nnesha

np good job!

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