Question

ab - c = 9

Answer 1

What do you want to do here?

Answer 2

solve for c

Answer 3

any ideas on how to do that?

Answer 4

no can you help me?

Answer 5

we want to isolate c

Answer 6

so we need to move over that 'ab' term

Answer 7

how do we do this?

Answer 8

umm i have no idea :/

Answer 9

ab - c = 9

0 + ab - c = 9

Do we add ab to both sides? or subtract ab from both sides?

Answer 10

i would say subtract

Answer 11

good

Answer 12

ab - c = 9


0 + ab - c = 9
- ab -ab


-c = 9 - ab

Answer 13

We're not done though. We want c and NOT -c

Answer 14

So how do we fix this?

Answer 15

divide negative c?

Answer 16

by what?

Answer 17

-c divided by <some number> = c

What is <some number> ???

Answer 18

9??

Answer 19

something negative divided by some number becomes positive

What is that "some number" ?

Answer 20

example

-12 divided by x = 12

what is x ?

Answer 21

-1?

Answer 22

good

Answer 23

So -c divided by -1 = c

Answer 24

so we must do this to both sides...or equivalently...we must do it to EVERY term

So divide every term by -1

Answer 25

so the problem you gave me was
ab - c = 9


0 + ab - c = 9
- ab -ab


-c = 9 - ab

Answer 26

yes, now divide everything by -1

Answer 27

to completely isolate c

Answer 28

so its -c= 9 -ab
-1 -1

like that?

Answer 29

Like this

\[\Large ab - c = 9\]

\[\Large ab - c = 9\\-ab \ \ \ \ \ \ \ \ \ \ \ \ \ -ab\]

\[\Large - c = 9-ab\]

\[\Large \frac{-c}{-1} = \frac{9}{-1}+\frac{-ab}{-1}\]

Answer 30

is it
-ab - 9

Answer 31

close....

Answer 32

9 divided by -1 = -9

Answer 33

but -ab divided by -1 is NOT -ab

Answer 34

because negative times a negative is a positive

Answer 35

and a negative divided by a negative = positive

Answer 36

so it would be 9 + ab?

Answer 37

no

Answer 38

9 divided by -1 = -9

Answer 39

ok let me try this again

Answer 40

ok

Answer 41

ab - 9

Answer 42

you got it

Answer 43

\[\Large ab - c = 9\]

\[\Large ab - c = 9\\-ab \ \ \ \ \ \ \ \ \ \ \ \ \ -ab\]

\[\Large - c = 9-ab\]

\[\Large \frac{-c}{-1} = \frac{9}{-1}+\frac{-ab}{-1}\]

\[\Large c = -9+ab\]

\[\Large c = ab-9\]

Answer 44

thanx for the help!

Answer 45

yw