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Question Number 146488 by mathdanisur last updated on 13/Jul/21

if   x+y=216   and   dcm(x;y)=18  find   x−y=?

ifx+y=216anddcm(x;y)=18findxy=?

Commented by mathdanisur last updated on 13/Jul/21

the biggest common divisot

thebiggestcommondivisot

Commented by gsk2684 last updated on 13/Jul/21

dcm means?

dcmmeans?

Answered by mathmax by abdo last updated on 13/Jul/21

x=qd and y=q^′ d with Δ(q,q^′ )=1    (d=18)  x+y=216 ⇒qd +q^′  d=216 ⇒q+q^′  =((216)/(18))=13  we get the system   { ((q+q^′  =13)),((Δ(q,q^′ )=1)) :}               q=1 ⇒q^′ =12  sol^o  ⇒x=18 and y=12×18=...  q=2⇒q^′  =11 sol^o  ⇒x=36 and y=11×18=...  q=3⇒q^′  =8 sol^o  ⇒x=3×18  and y=8×18  q=4 ⇒q^′  =9  sol^o  ⇒x=4×18 and y=9×18  q=5 ⇒q^′  =8 sol^o  ⇒x=5×18 and y=8×18  q=6 ⇒q^′  =7  sol^o ⇒x=6×18 and y=7×18  now you can find x−y....(dont forget symetrie of the system!)

x=qdandy=qdwithΔ(q,q)=1(d=18)x+y=216qd+qd=216q+q=21618=13wegetthesystem{q+q=13Δ(q,q)=1q=1q=12solox=18andy=12×18=...q=2q=11solox=36andy=11×18=...q=3q=8solox=3×18andy=8×18q=4q=9solox=4×18andy=9×18q=5q=8solox=5×18andy=8×18q=6q=7solox=6×18andy=7×18nowyoucanfindxy....(dontforgetsymetrieofthesystem!)

Commented by mathdanisur last updated on 13/Jul/21

thanks Ser, but answer 90;126

thanksSer,butanswer90;126

Commented by Rasheed.Sindhi last updated on 15/Jul/21

mathmax sir  In 2nd line a typo:  x+y=216 ⇒qd +q^′  d=216 ⇒q+q^′  =((216)/(18))=12

mathmaxsirIn2ndlineatypo:x+y=216qd+qd=216q+q=21618=12

Answered by Rasheed.Sindhi last updated on 13/Jul/21

   x+y=216   and   gcd(x,y)=18  Let x=18u & y=18v where gcd(u,v)=1  x+y=216⇒18u+18v=216  ⇒u+v=12      (u,v)=(1,11)=(5,7)=(7,5)=(11,1)  u−v=−10,−2,2,10  x−y=18u−18v=18(u−v)             =18(−10),18(−2),18(2),18(10)  x−y=−180,−36,36,180

x+y=216andgcd(x,y)=18Letx=18u&y=18vwheregcd(u,v)=1x+y=21618u+18v=216u+v=12(u,v)=(1,11)=(5,7)=(7,5)=(11,1)uv=10,2,2,10xy=18u18v=18(uv)=18(10),18(2),18(2),18(10)xy=180,36,36,180

Commented by mathdanisur last updated on 13/Jul/21

thanks Ser, but 90;126

thanksSer,but90;126

Commented by Rasheed.Sindhi last updated on 13/Jul/21

Your answers seem wrong to me.   x+y=216(given)  If x−y=90(your answer)    x=153 ,y=63  gcd(153,63)=9≠18   Similarly      x+y=216(given)  If x−y=126(your answer)  x=171 ,y=45     gcd(171,45)=9≠18

Youranswersseemwrongtome.x+y=216(given)Ifxy=90(youranswer)x=153,y=63gcd(153,63)=918Similarlyx+y=216(given)Ifxy=126(youranswer)x=171,y=45gcd(171,45)=918

Commented by mathdanisur last updated on 13/Jul/21

good Ser, thanks

goodSer,thanks

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