Question

pls explain it how this formula derived. Class XI
pls fast...
Also suggest how to prepare for IIT when u are in class Class XI

Answer 1

Here , you have to use ' dot product of two vectors' .
As you know,
Dot product of two vectors A and B = |A|.|B|cos {theta}
where |A| and |B| are the magnitude of A and B . And {theta} is the angle Between A and B.

{alpha} is angle between A and positive x-axis.
so, dot product of A and x-axis.
Here,
A = xi + yj +zk
x-axis = i
A.i = |A|.|i|cos {alpha}
we know,
|A| = sqrt {x^2 +y^2 +z^2}
|i| = sqrt {1^2} = 1 put it above .

(Xi + yj + zk).(i +0j +0k)= sqrt {x^2 +y^2+z^2}.1cos {alpha}
x.1 + y.0 + z.0 = sqrt {x^2 + y^2 + z^2} cos{alpha}
cos {alpha} = x/sqrt {x^2+y^2+z^2}

Similarly you can deprive
Cos {beta} = y/sqrt {x^2+y^2+z^2}
Cos {gama}= z/sqrt {x^2+y^2+z^2}



IIT ( Indian institute of technology ) is the best platform for science loving students. For admission it conducts entrance exam .i.e. Jee-main & advanced . For entry you have to require qualify in both tests.

Some tips.
1.Jee asks basically numerical type questions. You have require to understand all concepts deeply.

2. Don't cheat with yourself . I mean if you are not understanding any concept or theory then clear your doubt briefly without any hazitations.

3. Increase creativity . I mean if you solve any question then you should create new method to solve that questions . This way you will gain skill to solve surprising questions by asking of JEE ADVANCED.

4. Believe yourself and potential. I mean that
Be positive .
Be confidence.
I can do it ( this sentence increase your excitement for doing new things .

5. Require effective ways for study.
I mean if you study then you should focus in only and only study.

Next ...

Next you also know how to study because you are in 11th . It means you can develop your mind for achieving your dreams .