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 #8
avatar+26400 
+5

OABC is a square. M is the mid-point of OA, and Q divides BC in the ratio 1:3. AC and MQ meet at P.  If O to A = a, O to C = c .  Express O to P in terms of a and c.

1.  $$\small{\text{
If $ \vec{Q} = \vec{c} + \frac{3}{4}\vec{a}
$ and $ \vec{M} = \frac{1}{2}\vec{a} $
so line $ \overline{MQ} $ is $\frac{1}{2}\vec{a} + \lambda ( \vec{Q}-\vec{M}) = \frac{1}{2}\vec{a} + \lambda (\vec{c}+\frac{1}{4}\vec{a}) $
}}$$

2.  $$\small{\text{
Line $ \overline{AC} $ is $\vec{a} + \mu ( \vec{c}-\vec{a}) $
}}$$

3.

$$\\\small{\text{
The intersection of the line $\overline{MQ}$ with the line $\overline{AC}$ is
}}
$\\$\small{\text{
the point $\vec{P} = \frac{1}{2}\vec{a} + \lambda (\vec{c}+\frac{1}{4}\vec{a}) $.}}
$\\$\small{\text{
We equate:
$
\frac{1}{2}\vec{a} + \lambda (\vec{c}+\frac{1}{4}\vec{a}) = \vec{a} + \mu ( \vec{c}-\vec{a})
$
}}
$\\$\small{\text{
so
$
\lambda (\vec{c}+\frac{1}{4}\vec{a}) - \mu ( \vec{c}-\vec{a}) = \frac{1}{2}\vec{a}
$
}}
$\\$\small{\text{
The perpendicular vector of $(\vec{c}-\vec{a})$ is $(\vec{c}+\vec{a})$, because we have a square and
}}
$\\$\small{\text{
$(\vec{c}-\vec{a}) * ( \vec{c}+\vec{a} ) = 0$, because the dot-product of vectors
}}
$\\$\small{\text{
perpendicular to each other is a Zero.
}}
$\\$\small{\text{
We multiply our equation with $( \vec{c}+\vec{a} )$ and see what passed:
}}$$

$$$\\$\small{\text{
$
\lambda (\vec{c}+\frac{1}{4}\vec{a}) (\vec{c}+\vec{a}) - \mu \underbrace{( \vec{c}-\vec{a}) (\vec{c}+\vec{a})}_{dot-product = 0} = \frac{1}{2}\vec{a} (\vec{c}+\vec{a})
$
}}
$\\$\small{\text{
Now we can dissolve after $\lambda$ and receive for $\lambda$:
}}
$\\$\small{\text{
$
\lambda = \dfrac{
\frac{1}{2}\vec{a} (\vec{c}+\vec{a}) }
{(\vec{c}+\frac{1}{4}\vec{a}) (\vec{c}+\vec{a})
}
$
}}
$\\$
\boxed{
\small{\text{
$\vec{P} = \frac{1}{2}\vec{a} + \lambda (\vec{c}+\frac{1}{4}\vec{a}) $}} = \lambda \vec{c} + (\frac{1}{2}+\frac{\lambda}{4})\vec{a}
$
}}}$$

 

Dec 11, 2014
 #1
avatar+33661 
+5
Dec 11, 2014
 #370
avatar+118723 
+8

@@ End of Day Wrap      Thurs 11/12/14       Sydney,   Australia         Time 6:10 pm          ♬

 

Hello everyone, 

 

It has been another busy day.  Great answers from Heureka, Alan, CPhill, Happy7, flflvm97, Nickdavis, shaniab29544, JMT3137681, hugekase, sasini, Alexa4life, geno3141, NinaTinasTwin, saseflower, SevenUp, Sorasyn and Zegroes.  Thanks everyone.

 

Here are some interest posts:

 

1) SevenUp tells us we can expect a play  

http://web2.0calc.com/questions/what-s-9-10-5-8

2) I should give this one some thought.  Thanks Heureka

 http://web2.0calc.com/questions/are-there-any-sequences-between-the-prime-numbers#r3

3) I great gif illustration of pi - Thanks flfvm97

http://web2.0calc.com/questions/what-is-pi_26

4 & 5) Exponential Growth   Thanks Alan

 http://web2.0calc.com/questions/a-countrys-population-in-1995-was-56-million-in-2002-it-was-59-million-estimate-the-population-in-2016-using-exponential-growth-formula-roun

http://web2.0calc.com/questions/a-culture-started-with-2-000-bacteria-after-4-hours-it-grew-to-2-200-bacteria-predict-how-many-bacteria-will-be-present-in-9-hours-round

6) This equation looks interesting       Thanks Chris  

http://web2.0calc.com/questions/solve-the-equation-and-find-the-roots-x-4-3-x-2-3-8-0

7) Simplifying complex numbers.       Melody and Chris

 http://web2.0calc.com/questions/7-cos330-i-sin330

 

That is it - thanks 

 

                  ♫♪  ♪ ♫                                ♬ ♬ MELODY ♬ ♬                                 ♫♪  ♪ ♫

Dec 11, 2014
 #186
avatar+118723 
0

Fri 12/11/14

 

1) This is hilarious.  Thanks happy.

http://web2.0calc.com/questions/i-ll-fix-mistakes-with-a-laugh#r4

2) I thought this was a good bit of light fun too.

http://web2.0calc.com/questions/how-does-an-apple-eat-10-apples-if-an-apple-is-one-apple

3) Vectors.  Thanks Heureka 

http://web2.0calc.com/questions/question-on-mechanics-vectors

4) This one looks really interesting  - CPhill bought it to my attention.   Thanks CPhill and Geno  

http://web2.0calc.com/questions/please-please-help-me

5) A great peice of 'trivia', can I say that?   Thanks Gino :))

http://web2.0calc.com/questions/why-1-1-2

6) Here is something that I have not seen before.  Thanks Gino and anon :)

http://web2.0calc.com/questions/what-is-2-tetrated-1-times

7) It seems flflvm97 is going to give us 'challenge questions'  This one does look intersting.

I don't find enough time to even answer 'real' questions.   Nevermind Chris found the time.  It (the time) must have been under his bed.  That is where you can find everything.  

http://web2.0calc.com/questions/flflvm-s-daily-question-day-2

8) Make x the subject in a quadratic. I liked this one :)

http://web2.0calc.com/questions/assigning-var#rr1

9) This puzzle question from flflvm97 created interest.  We have had it berfore I am sure but if I can't find it in our puzzles I will add it.  I have given it the green puzzle symbol.  Thanks flflvm97

http://web2.0calc.com/questions/flflvm-s-daily-question

10) Physics - Is  the weight of a ball relevant to high high it will bounce? Why, Why not? 

Thanks to Melody and flflvm97and especially Alan  

http://web2.0calc.com/questions/physics-and-maths-stuff

11) Number puzzle - suitable for everyone.

http://web2.0calc.com/questions/what-would-the-equation-be-to-a-solution-equaling-39-if-you-use-the-digits-1-9-8-2

12) Riddle - Nothing like a good riddle :)  Thans anon and Happy

http://web2.0calc.com/questions/riddle-5

                  ♫♪  ♪ ♫                                ♬ ♬ MELODY ♬ ♬                                 ♫♪  ♪ ♫

Dec 11, 2014
 #3
avatar+118723 
+5
Dec 11, 2014
 #1
avatar+118723 
+5
Dec 11, 2014

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