- #1

- 172

- 0

kx^(2) = 2mgh + 2mgx

become this

kx^(2) - 2mgh - 2mgx = 0

i thought it's

kx^(2) = 2mgh + 2mgx

0 = 2mgh + 2mgx - kx^(2) ???

on page 24:

(https://docs.google.com/viewer?a=v&...Bl-afE&sig=AHIEtbSu5IlwxnJBO0IoW60ISpyd0856Sg)

- Thread starter nchin
- Start date

- #1

- 172

- 0

kx^(2) = 2mgh + 2mgx

become this

kx^(2) - 2mgh - 2mgx = 0

i thought it's

kx^(2) = 2mgh + 2mgx

0 = 2mgh + 2mgx - kx^(2) ???

on page 24:

(https://docs.google.com/viewer?a=v&...Bl-afE&sig=AHIEtbSu5IlwxnJBO0IoW60ISpyd0856Sg)

- #2

NascentOxygen

Staff Emeritus

Science Advisor

- 9,244

- 1,072

SubtractHow did this:

kx^(2) = 2mgh + 2mgx

You can do it that way, too. Now multiply every term on both sides by -1i thought it's

kx^(2) = 2mgh + 2mgx

0 = 2mgh + 2mgx - kx^(2) ???

- #3

- 172

- 0

why do we need to mult both side by -1?Subtract2mghfrom both sides, then subtract2mgxfrom both sides

You can do it that way, too. Now multiply every term on both sides by -1

- #4

NascentOxygen

Staff Emeritus

Science Advisor

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That gets you the equation that you were expecting to see, but by a different route.why do we need to mult both side by -1?

- #5

- 172

- 0

That gets you the equation that you were expecting to see, but by a different route.

but what if you dont know the correct equation?

If i was doing this problem from scratch (without solution manuel)

I wouldnt have known this equation [0 = 2mgh + 2mgx - kx^(2)] was wrong because algebraically, i am correct.

is it like instincts from reading the problem to know what kind of equation to expect or something???

- #6

- 380

- 7

Do you want to solve for x or what?How did this:

kx^(2) = 2mgh + 2mgx

become this

kx^(2) - 2mgh - 2mgx = 0

- #7

- 172

- 0

yes.Do you want to solve for x or what?

- #8

- 380

- 7

Okay, now you got kx^(2) - 2mgh - 2mgx = 0 so you can useyes.

- #9

NascentOxygen

Staff Emeritus

Science Advisor

- 9,244

- 1,072

It's not wrong. It's perfectly correct.but what if you dont know the correct equation?

If i was doing this problem from scratch (without solution manuel)

I wouldnt have known this equation [0 = 2mgh + 2mgx - kx^(2)] was wrong because algebraically, i am correct.

In general, it is customary to arrange the terms in decreasing degree, and with the leading term having a positive coefficient, e.g., x

But this is just for appearances (and it makes it easier to comprehend), it's not wrong if you don't do this.

Multiplying both sides does not change anything material. If you do the same thing to both sides of an equation, you change nothing.

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