# Search results

1. ### Electric charge of capacitor

Yes gneill, but still that doesn't solve the problem. Does this mean the book didn't give enough data?
2. ### Electric charge of capacitor

Homework Statement Dielectric medium inside capacitor consists of two types (check the pic). Capacitor's plates are connected to a source of constant tension U. Distance between the plates is d and their area is S. Find the electric charge of capacitor's plates. Data given: U=500 V, d=2cm...
3. ### Finding the partial derivatives of function

Can you explain me why f_y(x-y) = -1\cdot f'(x-y)? I don't get it. What is then f_x(x+y) = ?
4. ### Finding the partial derivatives of function

Homework Statement If z=\frac{1}{x}[f(x-y)+g(x+y)], prove that \frac{\partial }{\partial x}(x^2\frac{\partial z}{\partial x})=x^2\frac{\partial^2 z}{\partial y^2} Homework Equations The Attempt at a Solution I don't know how I'm supposed to find the partial derivative of z with respect to...
5. ### Trigonometric limit problem

Yeah, I realized, after I posted this thread, that author added and substracted cosx in numerator. This was the trick. The problem is solved.
6. ### Trigonometric limit problem

Homework Statement Find \lim_{x \to 0}\frac{1-cosxcos2xcos3x}{1-cosx} The Attempt at a Solution Actually my book gives this continuation \lim_{x \to 0}\frac{1-cosx+cosx[1-cos2x+cos2x(1-cos3x)]}{1-cosx} but I don't know how author arrived there. Can anyone explain it to me? Thank you
7. ### Plane geometry problem

Homework Statement Find the equation of plane which contains the line l:\left\{\begin{array}{l} x=t+2 \\y=2t-1\\z=3t+3 \end{array}\right., and makes the angle of \frac{2\pi}{3} with the plane \pi:x+3y-z+8=0. The Attempt at a Solution My attempt was to find the normal vector of plane which...
8. ### Triple product vector problem

Hi tinytim, I see now that the vectors are lineary dependent so 0 is the right answer. I just want to have this question answered, are these operations I did legal? Thank you
9. ### Triple product vector problem

Hello Ray, I did these operations: (-11\vec{m}\times\vec{n})\cdot(2\vec{m}+7\vec{n})=(-11\vec{m}\times\vec{n})\cdot2\vec{m}+(-11\vec{m}\times\vec{n})\cdot7\vec{n}= =-22(\vec{m}\times\vec{n})\cdot\vec{m}-77(\vec{m}\times\vec{n})\cdot\vec{n} So, according to definition, the vector...
10. ### Triple product vector problem

mxm and nxn by the definition gives us 0. That doesn't change anything.
11. ### Triple product vector problem

Find (\vec{a}\times \vec{b})\cdot \vec{c} if \vec{a}=3\vec{m}+5\vec{n}, \vec{b}=\vec{m}-2\vec{n}, \vec{c}=2\vec{m}+7\vec{n}, |\vec{m}|=\frac{1}{2}, |\vec{n}|=3, \angle(\vec{m},\vec{n})=\frac{3\pi}{4} This is my approach...
12. ### Projection of line on plane

Homework Statement Given \pi: \begin{cases}l_1: \frac{x-2}{4}\ = \frac{y-1}{2}\ = \frac{z+5}{-4} &\\l_2: \frac{x+4}{-2}\ = \frac{y+1}{0}\ = \frac{z}{1} & \end{cases} and the point M=(1,2,3) outside the plane. Find the projection of the line M_1P on plane \pi where P is the intersection point...
13. ### Integral solving software?

Hello, Is there any software which solves integrals STEP BY STEP? Thank you.
14. ### C/C++ C++ random numbers!

Hello! I've solved my problem. I've been looking for this part of code: srand(time(NULL)); random = arr[rand() % (sizeof(arr) / sizeof(arr[0]))]; Thank you.
15. ### C/C++ C++ random numbers!

Hi borek, can you show me an example? Thank you.
16. ### C/C++ C++ random numbers!

Hello! I've been trying to create an algorithm which picks a number randomly from array. P.S i have an array like A={1,4,-1,3,-7,2,-14} and I want to pick a number randomly from array. Any idea? Thank you.
17. ### Archimedes principle problem.

Hello all! Inside the water, body weights two times less than in air. Density of water is 1000kg/m^3. Find the density of body. 1. Well I tried this solution and I'm not sure if it's correct. I started from this principle Fa=W/2 (inside water force equals weight of the body divided by...
18. ### Redox question

Borek, (it means "pie" in my language), thanks for the answer. I am just a type of autodidact, (i left school) so I'm just trying to get some things right. (Including tuning of my thinking). Thank you again. :)
19. ### Redox question

So it doesn't matter how atoms has O, oxidation number is always -2. This rule appears for all other elements right? So for O4, O3, and O2, we have -2, what am I going to do for H2SO4, because H2 is +2 and O4 -2, so S is not going to have any oxidation number? I would be very happy if you do...
20. ### Redox question

Hi Borek, I tried first this way: \text{H}_2{SO}_4 + \text{CaCO}_3 \rightarrow \text{CaSO}_4 + \text{CO}_2 + \text{H}_2{O} ON THE LEFT SIDE: For \text{H}_2{SO}_4 (oxidation numbers are: H is +1, S is +6 and O4 -8) For \text{CaCO}_3...
21. ### Redox question

Hi there, I have some trouble understanding redox reactions. Here is the question: Sulphuric acid is one of the strongest inorganic acides which in some reaction shows oxidation properties. In which of reactions below, sulphuric acid acts as oxidating tool? A. \text{H}_2{SO}_4 +...
22. ### Equation of normal

So the normal vector has the same direction as line. So how to find that vector and t?
23. ### Tides question

Thank you all. http://www.math.nus.edu.sg/aslaksen/teaching/tides.html Is this explanation correct? My book uses centrifugal force to explain the tides. Thank you for your contribution.
24. ### Equation of normal

No, can you help me with this and line of intersection? Thank you.
25. ### Equation of normal

Let me understand this. I have to create a plane which passes through that point. Another point is point of intersection. But to find that point i must have a direction vector of that plane and I don't have so can you help me with point of intersection. How can i find it? So, when I have that...
26. ### Equation of normal

Write equation of normal from point M(2,3,1) into line:l: \frac{x+1}{2}=\frac{y-0}{-1}=\frac{z-2}{3}. I just have no idea about this problem. Any hint? Thank you.
27. ### Tides question

Hi all! I was just wondering if anyone can explain me why the tides (created by moon effect) are created on opposite sides. (image is on attachment) Thank you.
28. ### Trouble with some terms.

Hi QuantumBend! I don't understand you. You didn't give a good explanation. Can somebody help me to understand these two terms and give me some basic example? Thank you.
29. ### Trouble with some terms.

Hi there! My physics teacher explained us a Ratherford model of atom and used some terms like "spin" and "quantic number". I'm havin trouble with these terms and maybe anybody can explain me the function of "quantic number" and spinnig and give me a basic example. I just visited some web...

31. ### Potential hole

Hi friends! Can somebody tell me anything about potential hole at liquids? Thank you!

Hi! for (int i=0; i<=9; i++) { for (int j=0; j<i; j++) cout << " "; for (int j=i; j<=9; j++) cout << "*" cout << endl; } Can anyone explain me what these lines are doing? Thank you!
33. ### Cin vs Scanf - C++ Input Comparison

use fgets(); :)
34. ### C program help

Hi guys! I made a program in C, which count vowels on text, but it doesn't work. Thats the code i have writed: #include <stdio.h> #include <string.h> int main() { char buffer[80]; int counter; printf("Enter a line of text: "); fgets(buffer, sizeof(buffer), stdin)...
35. ### Printf debugging

Hi there, I'm noob at programming. Can anyone explain me why we need printf debugging, how to implement it, and for what is used it? Thank you
36. ### Polynomes problem

Thank you guys, it's good to meet good mathematicans :)
37. ### Polynomes problem

Hi there, can anyone tell me how to resolve this problem? (4x^3 - 8x^3 + 7x - 2) : (2x^2 - 3x + 2) Thnx