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Question Number 95394 by I want to learn more last updated on 24/May/20

Solve:   x  +  y  =  3      .... (i)                 x^y   +  y^x   =  6    .....  (ii)

Solve:x+y=3....(i)xy+yx=6.....(ii)

Commented by mr W last updated on 25/May/20

no solution.  from (ii):  x^y +y^x =6 ⇒x+y≥((2 ln 3)/(W(ln 3)))≈3.651  but from (i):  x+y=3

nosolution.from(ii):xy+yx=6x+y2ln3W(ln3)3.651butfrom(i):x+y=3

Commented by I want to learn more last updated on 25/May/20

Wow please sir.  What of            x  +  y   =  5        ......  (i)           x^y   +  y^x    =  17      ...... (ii)  x  =  2  and  y  =  3.  Please sir show the part.  Thanks sir.

Wowpleasesir.Whatofx+y=5......(i)xy+yx=17......(ii)x=2andy=3.Pleasesirshowthepart.Thankssir.

Commented by mr W last updated on 25/May/20

x+y≥((2 ln ((17)/2))/(W(((17)/2))))≈4.841  with x+y=5>4.841 there are two  solutions: x=2,y=3 or x=3,y=2.  in this case the solutions are obvious.  we can not calculate them using a  formula. for example for x+y=6   the solutions are no longer obvious.  you can get them only approximately.

x+y2ln172W(172)4.841withx+y=5>4.841therearetwosolutions:x=2,y=3orx=3,y=2.inthiscasethesolutionsareobvious.wecannotcalculatethemusingaformula.forexampleforx+y=6thesolutionsarenolongerobvious.youcangetthemonlyapproximately.

Commented by I want to learn more last updated on 25/May/20

Thanks sir. I appreciate.

Thankssir.Iappreciate.

Commented by I want to learn more last updated on 25/May/20

How do we separate    x + y  to  get     x  +  y   ≥   ((2 ln(((17)/2)))/(W(((17)/2))))   sir

Howdoweseparatex+ytogetx+y2ln(172)W(172)sir

Commented by I want to learn more last updated on 25/May/20

Because i see questions like:      x^x   +  y^y   =  31      ..... (i)         x  +  y   =   5       .... (ii)  So, i was wondering if any method could solve it.  x  =  2   and  y  =  3

Becauseiseequestionslike:xx+yy=31.....(i)x+y=5....(ii)So,iwaswonderingifanymethodcouldsolveit.x=2andy=3

Commented by mr W last updated on 25/May/20

let′s look at x^y +y^x =a with a>0  this curve is symmetric about y=x.  let′s look at x+y=b, it′s a line   perpendicular to y=x.  see picture:

letslookatxy+yx=awitha>0thiscurveissymmetricabouty=x.letslookatx+y=b,itsalineperpendiculartoy=x.seepicture:

Commented by mr W last updated on 25/May/20

Commented by I want to learn more last updated on 25/May/20

Thanks sir. I appreciate

Thankssir.Iappreciate

Commented by mr W last updated on 25/May/20

we find a line x+y=k which tangents  the curve x^y +y^x =a at point A.  if x+y=b<k ⇒no solution.  if x+y=b=k ⇒one solution.  if x+y=b>k ⇒two solutions.    say point A(p,p), we have  p^p +p^p =a  p^p =(a/2)  ((ln ((a/2)))/p)e^((ln ((a/2)))/p) =ln ((a/2))  ⇒((ln ((a/2)))/p)=W(ln (a/2))  ⇒p=((ln (a/2))/(W(ln (a/2))))  line x+y=k passes through A(p,p)  ⇒k=2p=((2 ln (a/2))/(W(ln (a/2))))

wefindalinex+y=kwhichtangentsthecurvexy+yx=aatpointA.ifx+y=b<knosolution.ifx+y=b=konesolution.ifx+y=b>ktwosolutions.saypointA(p,p),wehavepp+pp=app=a2ln(a2)peln(a2)p=ln(a2)ln(a2)p=W(lna2)p=lna2W(lna2)linex+y=kpassesthroughA(p,p)k=2p=2lna2W(lna2)

Commented by I want to learn more last updated on 12/Dec/20

Sir, for      x^x   +  y^y   =   a       and     x  +  y  =  b,  Please how can we know it is solvable just like the above:  x^y   +  y^x   =  a,   x  +  y  =  b.

Sir,forxx+yy=aandx+y=b,Pleasehowcanweknowitissolvablejustliketheabove:xy+yx=a,x+y=b.

Commented by I want to learn more last updated on 12/Dec/20

Sir what of     x^x   +  y^y   =  a,     and   x  +  y  =  b.  How can we know it is solvable like the one you showed above.

Sirwhatofxx+yy=a,andx+y=b.Howcanweknowitissolvableliketheoneyoushowedabove.

Commented by mr W last updated on 12/Dec/20

Commented by I want to learn more last updated on 12/Dec/20

Commented by I want to learn more last updated on 12/Dec/20

Sir, i mean is it still the same as this.

Sir,imeanisitstillthesameasthis.

Commented by mr W last updated on 12/Dec/20

you can proceed in similary way, but  not exactly the same way.

youcanproceedinsimilaryway,butnotexactlythesameway.

Commented by I want to learn more last updated on 13/Dec/20

Thanks sir.

Thankssir.

Commented by I want to learn more last updated on 13/Dec/20

Sir, i will really love it if you can show me sir.  Am sorry to be taking your time. Please help me sir.

Sir,iwillreallyloveitifyoucanshowmesir.Amsorrytobetakingyourtime.Pleasehelpmesir.

Commented by Tawa11 last updated on 19/Jul/21

Sir mrW, i searched old post. Please show this sir. It is similar to  my question:    x^x   +  y^y   =  13,    x  +  y  =  5.  I will love to just know the conditions if the question is solvable or not.  Just as you showed above. Thanks sir.

SirmrW,isearchedoldpost.Pleaseshowthissir.Itissimilartomyquestion:xx+yy=13,x+y=5.Iwilllovetojustknowtheconditionsifthequestionissolvableornot.Justasyoushowedabove.Thankssir.

Commented by mr W last updated on 20/Jul/21

i have already said.

ihavealreadysaid.

Commented by mr W last updated on 20/Jul/21

you can use the method above and  you should get that x^x +y^y =13 and  x+y=5 have no solution.

youcanusethemethodaboveandyoushouldgetthatxx+yy=13andx+y=5havenosolution.

Commented by Tawa11 last updated on 20/Jul/21

I will try sir.

Iwilltrysir.

Commented by Tawa11 last updated on 20/Jul/21

Thanks God bless you.

ThanksGodblessyou.

Commented by Tawa11 last updated on 25/Jul/21

Sir, please help me. I am not getting it.  Please.

Sir,pleasehelpme.Iamnotgettingit.Please.

Commented by Tawa11 last updated on 25/Jul/21

Please!!!

Please!!!

Commented by mr W last updated on 25/Jul/21

i have said all what i can say and what  i know. you know the graph of  x^y +y^x =a and that for x^x +y^y =a and  you know when the line x+y=b   intersects these graphes and then  get if there is a solution or two  solutions or no solution. i put all  this in following diagram:

ihavesaidallwhaticansayandwhatiknow.youknowthegraphofxy+yx=aandthatforxx+yy=aandyouknowwhenthelinex+y=bintersectsthesegraphesandthengetifthereisasolutionortwosolutionsornosolution.iputallthisinfollowingdiagram:

Commented by mr W last updated on 25/Jul/21

Commented by mr W last updated on 25/Jul/21

you have a=13,  k=((2ln (a/2))/(W(ln (a/2))))=((2 ln ((13)/2))/(W(ln ((13)/2))))=4.552  x+y=5 > 4.552  you can get from the diagram that  x^x +y^y =13 and x+y=5 have no solution.

youhavea=13,k=2lna2W(lna2)=2ln132W(ln132)=4.552x+y=5>4.552youcangetfromthediagramthatxx+yy=13andx+y=5havenosolution.

Commented by mr W last updated on 26/Jul/21

for the same reason you can get that  x^y +y^x =13 and x+y=5 have two solutions.  but there is no way to calculate the  exact solutions. they can only be  approximated.

forthesamereasonyoucangetthatxy+yx=13andx+y=5havetwosolutions.butthereisnowaytocalculatetheexactsolutions.theycanonlybeapproximated.

Commented by Tawa11 last updated on 26/Jul/21

God bless you sir. I really appreciate your time. Long life and good health  and wealth.

Godblessyousir.Ireallyappreciateyourtime.Longlifeandgoodhealthandwealth.

Commented by Tawa11 last updated on 09/Aug/21

Sir, I have solved:      x^y    +   y^x    =   13      and    x  +  y   =   5.  I  got        x   ≈   1.672      and     y   ≈   3.328

Sir,Ihavesolved:xy+yx=13andx+y=5.Igotx1.672andy3.328

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