160 - Mathematics Questions Answers

What is the range of the function  y = (e^-x)/ (1+[x]) is ?

Asked By: AMIT DAS
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Joshi sir comment

Domain of the given function is (-∞, -1) υ [0, ∞)

Now at x=0, y=1

and at x=∞, y=0

similarly left limiting value of y = -e

and for x=-∞, y=-∞

so range is (-∞, -e] υ (0, 1]

Maths >> Vector and 3-D >> Plane AIEEE

line AB intersects CD internally in the ratio K : 1  where K is undefined , these line may be  ( 1) concurrent  ,   (2)  intersecting ,  (3) skew  <  (4)  all of these .     explain plese   ?

 

 

Asked By: SHUBHAM VED
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Joshi sir comment

I think it will be skew because skew lines do not intersect in real points 

If the lines represented by 2x²-5xy+2y² =0 , be the two sides of a || gm and the line  5x+2y=1 be one of teh diagonals. then  the equation of the other diagonal is ?

Asked By: AMIT DAS
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Joshi sir comment

2x²-5xy+2y² =0

=> (x-2y)(2x-y) = 0 

these 2 lines pass through origin so one of the diagonal will definitely pass through origin. Given diagonal does not contain origin so second diagonal will pass through origin.

For finding any other point in the second diagonal first solve the two lines with given diagonal one by one. After calculating the two vertax use the formula for middle point of given diagonal. This point will be present in the second diagonal also. 

 

 

The AM of two positive numbers a & b exceeds their GM by 3/2 & the GM exceeds the HM by 6/5 such that a+b= α , |a-b|=β , then which of them are correct,

1) α + β² = 96            2) α + β² =74          3)α²+β = 234         4)α²+β = 84 

Asked By: AMIT DAS
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Joshi sir comment

(a+b)/2 = √ab + 3/2                   (1)                        or         a+b = 2√ab + 3

√ab      = 2ab/(a+b)  +  6/5       (2)                        or         5(a+b)√ab  =  10ab + 6(a+b)      

on solving these 2 we get               5[2√ab + 3]√ab = 10ab + 6[2√ab + 3]

                                           or               10ab + 15√ab  =  10ab + 12√ab + 18

                                           or                3√ab = 18     or      ab = 36          and      a+b = 15 = α

 so a-b = √(225 - 144)     =    √81     =     9 = β

if x,y,z are acute and cos x= tan y , cos y = tanz , cos z = tan x, then the value of sin x is ;

Asked By: AMIT DAS
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Joshi sir comment

 

by 1st equation  sec y = √(1+cos2x)  so cos y = 1/ √(1+ cos2x)

by 3rd equation sec z = cot x  so  tan z = √(cot2x - 1)

on putting these 2 values in 2nd equation we get  

1/ √(1+ cos2x) = √(cot2x - 1)

so sin2x = (1+cos2x)(cos2x-sin2x)

or sin2x = (2-sin2x)(1-2sin2x)

or sin2x = 2-4sin2x-sin2x+2sin4x

or 2sin4x-6sin2x+2 = 0

now solve it for sinx 

Maths >> Calculus >> Integrations IIT JEE

0π [cot-1x]dx

Asked By: NIKHIL VARSHNEY
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Joshi sir comment

i think the question will be 0π [cotx]dx because limits are in angular terms.

by graph given below we get answer as -π/2

here in the graph same coloured shaded region are dx*(-1) always, because for every similar pair [+k]+[-k] = -1 , here k is a real number, so complete area = -1(π/2)

(α,β);(β,γ) &(γ,α) are respectively the roots of x²-2px+2=0, x²-2qx+3=0,x²-2rx+6=0. if α,β,γ are all positive , then the value of p+q+r is 

Asked By: AMIT DAS
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Joshi sir comment

According to the given conditions

α+β=2p      (1)                 α*β=2        (2)

β+γ=2q       (3)                 β*γ=3        (4)

γ+α=2r       (5)                  γ*α=6        (6)

so α+β+γ = p+q+r              (7)

and α*β*γ=6                       (8)

dividing eq. (8) by (2), (4) , (6)  one by one we will get α, β, γ    hence we will get p+q+r

 

If     a sinx + b cos(x+θ) + b cos(x-θ) = d, then the minimum value of |cos θ| is equal to :

sir i have expanded cos(x+θ) & cos(x-θ) and after that i got the equation: (d sec x - a tanx)/2b = cos θ. now , can i write  minimum value of (d sec x -a tanx) = (d²-a²)^(1/2).. as all the options contain (d²-a²)^(1/2).......or do tell the other hint to solve it..

Asked By: AMIT DAS
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Joshi sir comment

Dear amit your starting steps are correct 

now let us consider that   d secx - a tanx  = y

on differentiating we will get d secx tanx - a sec2x = dy/dx

on comparing with 0 we get d tanx = a secx       or               sinx = a/d               so         secx = d/√(d2-a2)           and   tanx = a/√(d2-a2)

so minimum of given expression = [d2/ √(d2-a2)] - [a2/√(d2-a2)]  =        √(d2-a2)   

left hand derivative of  f(x) = [x]sin( pie x) at x=k where k is an integer,

Asked By: SHUBHAM VED
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Joshi sir comment

 

Left hand derivative of given function at x = k (k is an integer) is

   limh -> 0 {f(k-h) - f(k)}/ {k-h-k}  

= lim-> 0 {[k-h] sin π(k-h) - [k] sin πk}/{-h}                  now 2 cases arise for even and odd k

 

first case

= limh ->0  (k-1) sin (-πh) - 0 / (-h)                          if k is even ,   here we used sin πk = 0 and sin (2π-x) = sin (-x) 

= π(k-1)                   here we used sin (-πx)/(-πx) = 1

   

second case

= limh->0 (k-1) sin (πh) - 0 / (-h)                            if k is odd,    here we used sin πk = 0 and sin (3π-x) = sin x

= -π(k-1) 

 

 

Solution by Joshi sir

 

Left hand derivative of given function at x = k (k is an integer) is

   limh -> 0 {f(k-h) - f(k)}/ {k-h-k}  

= lim-> 0 {[k-h] sin π(k-h) - [k] sin πk}/{-h}                  now 2 cases arise for even and odd k

 

first case

= limh ->0  (k-1) sin (-πh) - 0 / (-h)                          if k is even ,   here we used sin πk = 0 and sin (2π-x) = sin (-x) 

= π(k-1)                   here we used sin (-πx)/(-πx) = 1

   

second case

= limh->0 (k-1) sin (πh) - 0 / (-h)                            if k is odd,    here we used sin πk = 0 and sin (3π-x) = sin x

= -π(k-1) 

so for even and odd k answer will be different.

     f(x)  = integraition of ( t2-t+2 )2005( t2-t-2 )2007( t2-t-6 )2009( t2-t-12 )2011( t2-3t+2 )2012  dt, then sum of values of x,  where maxima of (x)    is

Asked By: SHUBHAM VED
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Joshi sir comment

I think the right question is  

f(x)  = 0( t2-t+2 )2005( t2-t-2 )2007( t2-t-6 )2009( t2-t-12 )2011( t2-3t+2 )2012  dt    

then sum of values of x,  where maxima of f(x) will be obtained is

for maxima f '(x) = 0

by using Newton Lebnitz formula we get

f '(x) =  (x2-x+2 )2005( x2-x-2 )2007( x2-x-6 )2009( x2-x-12 )2011( x2-3x+2 )2012

comparing it with 0 and making factors we will get x = -1, 2, 3, -2, 4, -3, 1

now obtain the maxima point then sum these values

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