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I have not worked this question out but I would most likely look at the different probabilities and then add them together

P(BB)

+ P(WW throw back and get BB) on second try)

+ P(BW throw back the white one and get a black next time)

+ P(WB throw back the white one and get a black next time)

Hi OldTimer :)

An aeroplane is observed at the same instant from three stations A,B, C in a horizontal straight line but not in a vertical plane through the aeroplane.

If AB=BC =c and the angles of elevation from A,B C are respectively  alpha, beta and gamma prove that the height of the plane is

\(\frac{c\sqrt2 }{\sqrt{(cot^2\alpha +cot^2\gamma -2cot^2\beta )} }\)

I have not got my head around what this question is asking.  Can you (or someone else) help with a pic?

this is the bit I am not understanding 

"a horizontal straight line but not in a vertical plane"

i agree with melody, 

since there are multiple formulas for solving quadratics, and it depends on what the context asks you to do! 

it's all good!! :) 
don't worry about it i know what you meant 

You need to explain the question better.

Notreallymath has asked if this is correct:

2a+2a+8=80

No, Not quite.  

--------

If    a    is the width then

The the length will be      a+8

This means that the perimeter will be     a+a+    a+8    +   a+8  = 4a+16

so

4a+16 = 80

But what I was getting at is that the perimeter is 2*length + 2*width

so a HALF of the perimeter is  length+ width

so

x + x+8 = 40

2x+8=40

2x     = 32

x = 16

so the width is 16   and the length is ??

You can do it either way though.    

Ohh! You are right! 

(-y,x) is correct for 90 degrees

(Sorry I always get confused with 90 degrees and 270 lol) 

Let length=x+8 

Width= x

Apply the perimeter formula for rectangle which is: 

2*(Length+Width) 

we already know that length=x+8 and width is x 

so,

2*(x+8+x)= 2*(2x+8) = 4x+16

well the perimeter as the question says is 80 inches

so set,

4x+16=80

subtract 16 from both sides

4x=64

divide by 4

x=16

Well width is x so it is 16

length= 16+8=24 

You can make sure by subistuting length and width in the perimeter formula

so

2*(24+16)=80

2*(40)=80

yes indeed these values work.

wait wait wait,,, 

i agree with everything you just said except for one thing... 


shouldn't 90 degree rotations do this to a point?? 

\((x,y)\rightarrow(-y,x)\)


but thank you for your help :) your answer was extremely clear to understand. 

thank you guys so much!!

So would it be 

2a+2a=8=80

Yes, it always says to me that but once you return to main page, your question/answer already posted

Hint,

If you let the width be x units long.  Then how long will the length be?

If the perimeter is 80 what will length + width be?

-(-6)+/-√-6^2-(4*2*3)

This could mean manz different things, but if this is what you intend ....

\(-(-6) \pm \sqrt{-6^2-(4*2*3)}\\ =+6 \pm \sqrt{-36-24}\\ =6 \pm \sqrt{-60}\\\)

There are no REAL solutions to this as yu cannot find the square root of a negative number.

The complex solutions are

\(=6\pm\sqrt{60}\;i\\ =6\pm2\sqrt{15}\;i\)

There a many ways, depending on the problem and the instructions.

Well, RIP Tiny Pic,

but even more.

RIP HISTORIC POSTS!

I agree with you guest! Very efficient! However, there might be multiple magnifying glasses....

Good job SVS. This problem uses Combination, and you might need to know the formula for this one, guest!

I am that guest just answered above, not the one who posted the question.

I would like to say this website is literally broken. When I posted as a guest, it said "internal server error"

There are tremondous amounts of other glitches, too.
 

Actually its kind of tricky? The question ONLY asks for the diameter of venus, so 7,520.8 mi

13c7=1716

Yeah, it was just a troll :D 

OK won't do it again 

John would have 15 apples. 

He would be moving at 30m/s 

The Diameter of Venus is 12,100 km

ps( I think this is a troll of some type but whatever lol)

(Try not to do this again) (even though its pretty funny )

For a rotation 90 degrees around the origin, switch the coordinates for example if it is: (x,y) it will be: (y,x) notice that y became x and x became y values.

In your example, 

-2,3 will be 3,-2 

Speaking of counterclockwise 

Yes, if we rotate 90 degrees it is already in counterclockwise, It is just there to confuse you. 

Wouldnt the points just return back to its original points, or am I mistaken?