Math Is Fun Forum

koothrapali

Member

Registered: 2011-06-03

Posts: 5

Triangle and Radical problem

A week or so ago I got this problem and have tried to solve it with no success.

I am supposed to find z, y and z so that xy=-6+2√2, xz=7+7√2 and yz=2-4√2.

Help!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

Hi koothrapali;

I am not sure that I am following you here. It looks like you just want to solve the 3 equations below?!

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,649

Re: Triangle and Radical problem

Or is this asking for the angles in this triangle?

In which case, (ignoring the two negative sides and plowing ahead anyway) by the cosine rule

No arccos available for this value, so it looks like I've wasted my time  doing this ... oh drat

wrt post #4. 

What the heck are you doing up?

Take the angles if you can not sleep

That's it in a nutshell.  You'd think this would have sent me to sleep but no.

Hopefully koothrapali  will put us out of our misery and explain what this question is after.

Bob

Last edited by Bob (2011-06-03 14:39:41)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

Hi Bob;

What the heck are you doing up?

Take the angles if you can not sleep.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

koothrapali

Member

Registered: 2011-06-03

Posts: 5

Re: Triangle and Radical problem

Sorry, very sorry. I am supposed to fing x, y and z so that the product of x and y is equal to -6+2√2, the product of xz is equal to 7+7√2 and the product of yz is equal to 2-4√2.

Again very sorry for not explaining.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

There are 2 solutions:

Or

But I still do not know why the triangle and what x,y,z are.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

koothrapali

Member

Registered: 2011-06-03

Posts: 5

Re: Triangle and Radical problem

Thank you bobbym! But one question, how did you get the answers? What was the procedure?

Last edited by koothrapali (2011-06-06 15:26:09)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

Solve in the first one for x

Substituting in 2.

Solve in the last eq for z

Substitute in this:

Solve for y

Now you have y. Just plug in to one of these

to get x or z.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

koothrapali

Member

Registered: 2011-06-03

Posts: 5

Re: Triangle and Radical problem

Thank you very much for your quick answer, and your patience.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

Hi koothrapali;

Your welcome.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

koothrapali

Member

Registered: 2011-06-03

Posts: 5

Re: Triangle and Radical problem

I found a new way to solve for y: multiply xy and yz, then divide by xz. It also works, I did it both ways. Thank you!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Triangle and Radical problem

Hi koothrapali;

Yes, that will work in this case! But as a general idea it should be done carefully, if at all.

Here it is obvious that xz can not be zero. Before you make the move of dividing by unknowns you should prove that they do not equal zero, and you should state that.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.