find a such that there is no real root

2 sin x= mod x + a

find a such that there is no real root

16 Answers

62
Lokesh Verma ·

no one?

Think this using graphs

6
Kalyan IIT-K Beware I'm coming ·

is it mod x +a or mod (x+a)

11
SANDIPAN CHAKRABORTY ·

if a is some integer then the value of a is 1(the lowest integer for which there is no solution...)

(i think its |x|+a)

6
Kalyan IIT-K Beware I'm coming ·

it sud be slightly above 2sinx
coz max value of 2sinx =2
so a will be from (2,∞)
bhaiya can dis be a solution??
no real root meaning graph of 2sinx will not cut mod x +a nytime

6
Kalyan IIT-K Beware I'm coming ·

@sandipan how did u make such a beautiful graph??/
it took a lot of pain for me to make d sinx graph in paint??

6
Kalyan IIT-K Beware I'm coming ·

ohh m sry sandipan ur right....
my graph is aweful ..so i got d right ans.......

11
SANDIPAN CHAKRABORTY ·

I used a software for plotting graphs...otherwise to draw the graphs of sin cos...becomes really painful in paint....

62
Lokesh Verma ·

sandipan why is the lowest value 1?

11
SANDIPAN CHAKRABORTY ·

I used a software for plotting graphs...otherwise to draw the graphs of sin cos...becomes really painful in paint....

in fact Kalyan u r rite...

a can range from 1 to infinity...

is rite bhaiya??

11
SANDIPAN CHAKRABORTY ·

Bhaiya i meant to say that the lowest integral value of a is 1.

becuase lowest integral value below 1 is zero...but at a=0 y=|x| cuts the graph of y=2sin x ....thus there would be some solution...

at a=1 y=|x|+1 does not cut the graph of y=2sin x so there's no solution...

62
Lokesh Verma ·

I din get the logic?

WHy?

YOu are missing the point!

11
SANDIPAN CHAKRABORTY ·

i got mixed up bhaiya ...... is it something because of this..???

LHS attains max at x = pi/2 ...maximum value = 2

so |(pi)/2| ≈ 1.7....

so minimum value of a is 1 so that R.H.S > L.H.S due to which no soln.

???

62
Lokesh Verma ·

no sandipan...

Think of it in one of the two ways..

a) Tangent
b) Maxima Minima!

Dont know if you are getting the clue!

11
SANDIPAN CHAKRABORTY ·

is it this Bhaiya??

y = 2 sin x

dy/dx = 2 cos x

now we now slope of y = |x| is tan 45o = 1 (considering only the part in the 1st quadrnt)

so 2 cos x = 1

x = (pi)/3

so y = √3

so we need the tangent at ((pi)/3 , √3)

so eqn of tangent comes out to be y = x + (√3 - (pi)/3)

now given y = x + a shud be above the tangent..for no solution..

so a > (√3 - (pi)/3) = 0.686

so least integral value of a is 1.

62
Lokesh Verma ·

yup perfect this time :)

11
SANDIPAN CHAKRABORTY ·

:) thanks for the hint Bhaiya [1][1][1]

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