Test:208 QNo:2

The no of real roots of 2x = x2+1 is:

16 Answers

1
pratik.dutta dutta ·

can u please explain with the help of the graph , how there are 3 solutions of 2x =x2+1.

3
msp ·

let f(x)=2x-(1+x2)

clearly f(x)=0 at x=0,1

we want to chek out whether there are some other roots

for f(2)<0 f(3)<0,f(4)<0 and f(5)>0

so there is a root in between (4,5)

1
tr-10077 billa ·

ans bol sale.

23
qwerty ·

LOL

49
Subhomoy Bakshi ·

let us see like this....i dnt kno if i can continue correctly till the end....but lemme try...

\frac{\partial }{\partial x}(2^x)=2^x.ln2\simeq 6.9(2^x)

\frac{\partial }{\partial x}(x^2+1)=2x

2x ≤ 6.9(2x)

equality holds at, 2x=6.9(2x)
solving this we get a value of x...
can any one solve this out???

after finding x, we find the value of 2x and x2+1

49
Subhomoy Bakshi ·

no...the above approach leads to nowhere...at least i got lost....

simply we can see that the two functions become equal at x=0 and x=1...
and there is a root b/w 4 and 5....so there are 3 roots.....

49
Subhomoy Bakshi ·

oh me!! that was exactly what msp solved.....sorry...[1][1]

49
Subhomoy Bakshi ·

can someone help me i am stuck up.....i am getting a weird graph for y=2x...
can someone draw the graph of y=2x for me...please...[1][1]

49
Subhomoy Bakshi ·

arre koi to help karo....please....

23
qwerty ·

it is similar to ex,

its just dat for x = 1 , y = 2 ,

for x=0 , y = 1

49
Subhomoy Bakshi ·

then we re getting 2 solutions from the graph isnt it.?.?.?.?.?.

49
Subhomoy Bakshi ·

oh no....yes got it!!![1][1]

the curves do meet at very distant place...they re indeed converging...

thnxx qwerty.....for ALL the help u gave...

49
Subhomoy Bakshi ·

i'll post the graphical solution tomorrow....aaj bahut niind aa rahi hai...for some inexplicable reason...bye all...[1]

1
harsh jain ·

compare graphs of diff. of functions,their sign interchanges thrice
at x=0 2x<2x log2
at x=1 2x>2x log2
at x>>1 , 2x<2x log2

1
subhamban ·

the ryt ans has to be 2
there are two solutions and not 3...........

1
johncenaiit ·

No subhambar......it is 3....

see the original graph using online grapher....

the 3rd point is around x=4.26

Your Answer

Close [X]