Physics, Chemistry, Mathematics Forums

How many numbers can be formed with the digits 1,2,3,4,3,2 and 1 so that the odd digits always occupy odd places? Answer is 18. I have considered from 2 digit number to 7 digit number since there is no point in talking about 1 digit number.Also, 8 digit number does not make any sense since there there are only 3 even numbers and 4 even places.Like this I am getting answer more than 18.Where am I wrong?

THE POSITIVE NUMBERS x and y SATISFY xy=1.THE MINIMUM VALUE OF
1/x^4 +1/4y^4.

Cahrges Q₁ and Q₂ lies inside and outside resp. of a closed surface S.Let E be the field at any point on S and @ be the flux of E over S,then which are correct options

(A) If Q₁ changes,both E & @ changes

(B) If Q₂ changes, E will change but @ will not change

(C) If Q₁=0 and Q₂ not=0 then E not=0 but @=0

(D) If Q₁=not0 and Q₂=0 then E =0 but @ not=0

in the following figure,if AD=DC=x
and BC=y.then AB=?
angleBAC =20
angleADC=100

Take the effect of bulging of earth and it's rotation in account.Consider the following statements:

A) There are points outside the earth where the value of g is equal to it's value at the equator.

B) There are points outside the earth where the value of g is equal to it's value at ther poles.

a)Both A and B are correct. b)A is correct but B is wrong. c)B is correct but A is wrong. d) Both A and B are wrong.Answer is b).  

What is the ground state configuration of Mn4+

[Ar]4s2 3d1 or [Ar]4s0 3d3

Please tell the reason and the source of information.

Assertion(A): A stone of mass m kg is dropped vertically down from the window of a train which is at rest and then the same stone is dropped from the window of the train accelerating with a m/s2. The net force in air acting on the stone is mg in both cases.

Reason (R): Vertical and horizontal motions are independent of each other in two dimensional projectile motion.

(A) Both A and R are individually true and R is the correct explanation of A

(B) Both A and R are individually true and R is not the correct explanation of A 

Ans:

Instead of using formula of derivative i.e.

Df(x)= lim_h-->0f(x+h)-f(x)/h

if we use

D*f(x)= lim_h-->0[{f(x+h)} ² -{f(x)}²]/h

then find:

1) D*f(x) if  f(x)=x/lnx

2)D*g(x)|_x=1 if g(x)= x^x

3)slope of tangent to the curve y=xe^-1/|x|  at point (1,1/e)

Two fixed points A and B are taken on the axes such that OA = a and OB = b. Two variable points A' and B' are taken on the same axes, find the locus of the intersection of AB' and A'B Given that OA+OA = OA'+OB'.

integrate with limits 0 to pie

1) x³log(sinx)

2) x/{1+(sinxcosx)}