Question

Solving Systems of Equations by Substitution.

1.
-3x + 3y = 4
-x + y = 3

2.
-5x - 8y = 17
2x - 7y = -17

Answer 1

@jim_thompson5910 @Nnesha

Answer 2

@mathstudent55

Answer 3

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?

Answer 4

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

Answer 5

yep yep right :=)

Answer 6

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

Answer 7

yep

Answer 8

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

Answer 9

yes so they cancel out

Answer 10

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

Answer 11

oh okay :)

Answer 12

and for the next one...

Answer 13

yep

Answer 14

we can figure out the value of x...

2x - 7y = -17
2x = -17 + 7y
2x / 2 = (-17 + 7x) / 2
x = -8.5 + 3.5x

Answer 15

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

Answer 16

yes sorry :)

Answer 17

its okay yep right

Answer 18

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

Answer 19

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.

Answer 20

well i don't understand the 3rd line

Answer 21

if i did 17 - 42.5 = -25.5

Answer 22

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

Answer 23

what do you mean by moving 42.5?

Answer 24

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

Answer 25

correct

Answer 26

so what i did was correct right?

Answer 27

\(\color{blue}{\text{Originally Posted by}}\) @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

Answer 28

oh yeah

Answer 29

my mistake :\

Answer 30

:=) doing gREAT

Answer 31

y = 1 right?

Answer 32

yep right!

Answer 33

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

Answer 34

gO_OD to go!

Answer 35

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

Answer 36

PHYSICS hmmmm not sure

Answer 37

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

Answer 38

ye sure!

Answer 39

okay. here it is...

Answer 40

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.)

Answer 41

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

Answer 42

okay thank you though :)

Answer 43

np good job!