xét:x=y=z=0" role="presentation" style="font-size: 13.696px; display: inline; position: relative;">:x=y=z=0:x=y=z=0 là no .Xét :x,y,z≠0" role="presentation" style="font-size: 13.696px; display: inline; position: relative;">:x,y,z≠0:x,y,z≠0,chia cả 3 pt lần lượt cho 5xy;7yz;4zx" role="presentation" style="font-size: 13.696px; display: inline; position: relative;">5xy;7yz;4zx5xy;7yz;4zx{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1" role="presentation" style="font-size: 13.696px; display: inline; position: relative;">⎧⎩⎨⎪⎪⎪⎪65(1x+1y)=1127(1y+1z)=143(1x+1y)=1{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1⇒1x+1y+1z=1312" role="presentation" style="font-size: 13.696px; position: relative;">⇒1x+1y+1z=1312
a,<div>xét:x=y=z=0" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">:x=y=z=0:x=y=z=0 là no .Xét :x,y,z≠0" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">:x,y,z≠0:x,y,z≠0,chia cả 3 pt lần lượt cho 5xy;7yz;4zx" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">5xy;7yz;4zx5xy;7yz;4zx</div><div>{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">⎧⎩⎨⎪⎪⎪⎪65(1x+1y)=1127(1y+1z)=143(1x+1y)=1{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1<br></div><div>⇒1x+1y+1z=1312" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">⇒1x+1y+1z=1312⇒1x+1y+1z=1312<br></div><div>đến đây chắc dễ r</div>a,<div>xét:x=y=z=0" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">:x=y=z=0:x=y=z=0 là no .Xét :x,y,z≠0" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">:x,y,z≠0:x,y,z≠0,chia cả 3 pt lần lượt cho 5xy;7yz;4zx" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">5xy;7yz;4zx5xy;7yz;4zx</div><div>{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">⎧⎩⎨⎪⎪⎪⎪65(1x+1y)=1127(1y+1z)=143(1x+1y)=1{65(1x+1y)=1127(1y+1z)=143(1x+1y)=1<br></div><div>&#x21D2;1x+1y+1z=1312" role="presentation" style="font-size: 16px; vertical-align: baseline; display: inline; word-spacing: 0px; position: relative;">⇒1x+1y+1z=1312⇒1x+1y+1z=1312<br></div><div>đến đây chắc dễ r</div>