CONCEPTUAL DOUBT

If f (x) is continuous and g (x) is discontinuous at x = a are then f (x) +/-- g (x) is discontinuous at x = a

now is this always true or depends on the case???

i'll give an eg. f(x) = 1/x ; g(x) = 1/x ; h(x) = f(x) - g(x);
then is h(x) cont. or discont at x=0;

17 Answers

1
voldy ·

is this fmultilpied y g or fog ?? sry for silly doubt

21
tapanmast Vora ·

oh k k..... thank u sir!!!!

62
Lokesh Verma ·

in that function is not defined at x=0

I can given another example where it is discontinuous.

f(x)=[x]

g(x)=1/[x]

both the above are defined for x>3

f(x).g(x) is 1 always

which is continuous at x=integer.

21
tapanmast Vora ·

hmmmmm....... k thnx.......

and sir wat abt the eg provided abov??

is h discont at x=0

62
Lokesh Verma ·

F(x).G (x) is not necessarily discontinuous.

trivial example F(x)=0 for all x

and G(x) is any discontinuous function.

21
tapanmast Vora ·

oh k fine so f + g ka to confirm ho gaya.....

sir can u pl. confirm it 4 f(X)*G(X) = H(X)

ie if F(X) = X ; G(X) = 1/X

11
Anirudh Narayanan ·

It is discontinuous.

Other similar examples are :

y=sinx.cotx at x=0

y= cosx.tanx at x=Ï€/2

tanxcotx at x=0 and π/2

21
tapanmast Vora ·

hey ani u may call me by "any" name dude naam mein kya rakha hai?? kam dekho!!! LOL...

hey guyz dont u think this is strange coz we are almost defining h(x) = 1 but in a diff meth..... then y shud it not b cont?????? i think its a matter of CONVENTION coz in case of h(x) = x/x ; limit exists......

BUT YEAH maybe i too feel it wud be discont.....

11
Anirudh Narayanan ·

Don't care whether it is f+g or f*g........If the elements are not defined then function is not defined.
Tapan (if i may call u that): second h(x) is also not defined

11
Anirudh Narayanan ·

H(x) is definitely disc. at x=0

21
tapanmast Vora ·

but yes eureka in da "f+g" post of urs i feel u r spot on!!!

then how f*g???

21
tapanmast Vora ·

its a really controversial questn that i hav posted as both sides seem correct and its da questn wat it is taken as in PURE MATHS.....

another similar thing happens wen u take f(x) = x ; g(x) = 1/x; h(x) = f(x) * g (x);

now will this be cont at x=0????????// [7]

11
Subash ·

yes ani it is discontinuous sorry

11
Anirudh Narayanan ·

There is a test in this website just involving this concept. All elements of the function must be defined.....even if they cancel each other out

24
eureka123 ·

if f is continous and g is discontinuous then f+g is never continuous.....[1]

11
Anirudh Narayanan ·

YA SUBASH.......it is 0 for all x≠0

For x=0, both f(x) and g(x) are induvidually not defined.......so h(x) is not defined [4]

11
Subash ·

hows that ani func is zero always

maybe it holds for non zero functions

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