Proportions

• Nov 29th 2007, 05:57 PM
OzzMan
Proportions
1. 3/x=x/?

2. 3/?=?/10

3. 13/z=z/?

4. ?/y=y/10

5. 10/?=?/13

6. 13/?=?/3

These proportions are very strange to me, but its the way the book has it layed out.

Directions say use theorems 7.2 and 7.3 which make no sense to me, but here they are:

7.2 In a right triangle, the length of the altitude to the hypotenuse is the geometric mean between the lengths of the two segments on the hypotenuse.

7.3 In a right triangle with an altitude to the hypotenuse, each leg is the geometric mean between the sum of the squares of the lengths of the legs.
• Nov 29th 2007, 06:37 PM
OzzMan
i guess my question is how do you find the ? for a problem like 3/x=x/?

once i know how to find the ? i can take it from there
• Nov 29th 2007, 07:15 PM
topsquark
Quote:

Originally Posted by OzzMan
i guess my question is how do you find the ? for a problem like 3/x=x/?

once i know how to find the ? i can take it from there

I would replace the ? with a variable, say y:
$\displaystyle \frac{3}{x} = \frac{x}{y}$

Multiply both sides by xy:
$\displaystyle 3y = x^2$ <--Otherwise known as "cross-multiplication."

$\displaystyle y = \frac{x^2}{3}$

You can do this kind of thing with all of them.

-Dan
• Nov 29th 2007, 09:56 PM
OzzMan
Wow another easy problem. Thanks for the help. The book was dumb imo to have ? marks instead of lettered variables.
• Nov 29th 2007, 11:54 PM
OzzMan
nvm these problems arent done by cross multiplication. i checked the answer in the back of the book and they got non variable answers for both variables. so i really have no idea now.
• Nov 29th 2007, 11:59 PM
janvdl
Quote:

Originally Posted by OzzMan
nvm these problems arent done by cross multiplication. i checked the answer in the back of the book and they got non variable answers for both variables. so i really have no idea now.

What answer does the book give?
• Nov 30th 2007, 08:08 PM
OzzMan
the books answer for the first one is 10, x=square root of 30

which im assuming the 10 is for the ?

but how are these answers correct. i see no logical way of them being correct. anyone know ?
• Nov 30th 2007, 11:46 PM
janvdl
Quote:

Originally Posted by OzzMan
the books answer for the first one is 10, x=square root of 30

which im assuming the 10 is for the ?

but how are these answers correct. i see no logical way of them being correct. anyone know ?

No i cannot see why it would be those answers specifically either.
• Dec 1st 2007, 02:05 PM
OzzMan
yes biggest question is how did they get 10 for the ? makes no sense.
• Dec 1st 2007, 06:58 PM
OzzMan
Sorry to post again on this post but if anyone knows how to do this, could you help me out. I'm really lost with this. Mostly how they solve for the ? in the first one.
• Dec 2nd 2007, 02:18 AM
janvdl
Quote:

Originally Posted by OzzMan
Sorry to post again on this post but if anyone knows how to do this, could you help me out. I'm really lost with this. Mostly how they solve for the ? in the first one.

You'll get an infraction for bumping :eek:

No, honestly I cannot see how they got those values.
These equations can be satisfied with just about any value. (Although it seems it has to be only positive values)

• Dec 2nd 2007, 06:34 PM
OzzMan
Well this is my brothers homework and its from his geometry book. I'm just curious.
• Dec 3rd 2007, 06:19 AM
topsquark
Quote:

Originally Posted by OzzMan
Well this is my brothers homework and its from his geometry book. I'm just curious.

If the solution for #1 does not contain an x then there is information missing.

These cannot be done as stated. (As several people have now informed you.)

-Dan