Math help please!!

[Skipadeedoodah]

So - here's the problem.

The length of a rectangle is 23 less than five times its width. The area of the rectangle is 42 cm squared. Find the dimensions.

This is how I have it set up...

W (5W - 23) = 42 cm sq.

Any idea how to solve this?? I haven't done math like this in years.

 

[..Glamorous..]

hang on, trying it.

 

[Mz Chaos]

The answer is peanut butter and jelly!!!

Was I close???

 

[venray]

7 by 6

5 x 6 = 30- 23 =7

7x 6 = 42

dont ask me to show my work...lol

 

[Skipadeedoodah]

Yeah I got the answer by guessing LOL I just tried to figure out what two numbers when multiplied made 42...and there weren't that many options...so i just kept plugging in my W until I found one that worked 😛

 

[venray]

Exactly how I did it

 

[..Glamorous..]

Hahah, That is exactly how I figured it out.

 

[Deadsea7777]

Is a second order equation, ax2 + bx + c = 0;

You use the formula, [-b+/- sqrt(b2-4ac)]/2a to get x

(23-5h)×h = 42
5h2 -23h -42 = 0
then:
[23+/- sqrt (232-4×5×42)]/ 2×5 = [23+/- sqrt (529+ 840)]/10 =

[23+/- sqrt(1369)]/10 = (23+/-37)/10 = 60/10 = 6. The other root is negative.

Then h = 6 and, area= 42 = 6 × length; then length is 7.

If you got a computer, guessing work equally well.

 

[Skipadeedoodah]

Is a second order equation, ax2 + bx + c = 0;

You use the formula, [-b+/- sqrt(b2-4ac)]/2a to get x

(23-5h)×h = 42
5h2 -23h -42 = 0
then:
[23+/- sqrt (232-4×5×42)]/ 2×5 = [23+/- sqrt (529+ 840)]/10 =

[23+/- sqrt(1369)]/10 = (23+/-37)/10 = 60/10 = 6. The other root is negative.

Then h = 6 and, area= 42 = 6 × length; then length is 7.

If you got a computer, guessing work equally well.

 

[Hapless Ticklee]

And don't forget to permutate all of the variables, storing them in a cool dry place away from sunlight.

 

[Perduabo]

Is a second order equation, ax2 + bx + c = 0;

You use the formula, [-b+/- sqrt(b2-4ac)]/2a to get x

(23-5h)×h = 42
5h2 -23h -42 = 0
then:
[23+/- sqrt (232-4×5×42)]/ 2×5 = [23+/- sqrt (529+ 840)]/10 =

[23+/- sqrt(1369)]/10 = (23+/-37)/10 = 60/10 = 6. The other root is negative.

Then h = 6 and, area= 42 = 6 × length; then length is 7.

If you got a computer, guessing work equally well.

.......Jesus Christ!

*head asplodes*

 

[Capnmad]

w (5w - 23) = 42


Multiply the stuff on the left times w:

w (5w - 23) = 42

5w^2 - 23w = 42

(^2 means "exponent 2" or "squared")


Bring your 42 on over, changing its sign from + to - since it's crossing the equals sign:

5w^2 - 23w - 42 = 0


Now you have a quadratic equation. Time to factor:

5w^2 - 23w - 42 = 0

*some fucking magic*

(5w + 7)(w - 6) = 0


Check your work:

w(5w) - 30w + 7w - 42 = 0

5w^2 - 23w - 42 = 0

Seems to work out. Time to move along...


(w - 6)(5w + 7) = 0

Now, if you knew what w was above, you'd solve for each parenthetical and multiply them, to come to zero. For our answer to be zero, that means at least one of the parentheticals must amount to zero.

Let's try the first one:

(w - 6) = 0

w = 6


The second:

(5w + 7) = 0

w = - 7/5


- 7/5 is implausible for your problem, so the value for w is 6.

 

[meangry]

We do not discuss the work of the devil in these parts.

 

[venray]

w (5w - 23) = 42


Multiply the stuff on the left times w:

w (5w - 23) = 42

5w^2 - 23w = 42

(^2 means "exponent 2" or "squared")


Bring your 42 on over, changing its sign from + to - since it's crossing the equals sign:

5w^2 - 23w - 42 = 0


Now you have a quadratic equation. Time to factor:

5w^2 - 23w - 42 = 0

*some fucking magic*

(5w + 7)(w - 6) = 0


Check your work:

w(5w) - 30w + 7w - 42 = 0

5w^2 - 23w - 42 = 0

Seems to work out. Time to move along...


(w - 6)(5w + 7) = 0

Now, if you knew what w was above, you'd solve for each parenthetical and multiply them, to come to zero. For our answer to be zero, that means at least one of the parentheticals must amount to zero.

Let's try the first one:

(w - 6) = 0

w = 6


The second:

(5w + 7) = 0

w = - 7/5


- 7/5 is implausible for your problem, so the value for w is 6.

all that to get an answer that can be arrived at in less than a minute without all the fluff.....

lol

 

[CrystalLight]

I seriously had a nervous breakdown just by reading this thread. 😛

 

[Capnmad]

all that to get an answer that can be arrived at in less than a minute without all the fluff.....

lol

I know... But quadratic equations were my friggin' nemesis in middle school, so when I see one, I must destroy/solve it... And I prefer to make sure they're done methodically, so I know I haven't effed up.

Besides, my teachers wouldn't have accepted any of that "I can't show my work" stuff -- believe me, I tried!!!

 

[Skipadeedoodah]

Ahh quadratic equations - I forgot all about those assholes.

Thanks Babe!

 

[nenezinho]

What a memory!!!

I actually loved these but today it´s been ages since i´ve tried to solve one 🙂

Today it´s more about excel formulas and vbasic script.....baaaahhh miss the good old math! 🙂

 

[Hapless Ticklee]

God, Quadratic Equations... it took me years to successfully forget that wretched formula.

Now life is about anything... just so long as Quadratic Equations aren't involved then all is well