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Nội dung: <blockquote data-quote="tho ngok" data-source="post: 72144" data-attributes="member: 59985"><img src="https://latex.codecogs.com/gif.latex?%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7Dxyz%20+%20x%20=%20%5Cfrac%7B%7B7z%7D%7D%7B3%7D%5C%5Cxyz%20+%20y%20=%208x%5C%5Cxyz%20+%20z%20=%20%5Cfrac%7B%7B9y%7D%7D%7B2%7D%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />Dễ thấy (x;y;z)=(0;0;0) là một nghiệm của hệ phương trình đã cho. Với <img src="https://latex.codecogs.com/gif.latex?x,y,z%20%5Cneq%200" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />, ta có hpt đã cho tương đương<img src="https://latex.codecogs.com/gif.latex?%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7Dxy%20+%20%5Cfrac%7Bx%7D%7Bz%7D%20=%20%5Cfrac%7B7%7D%7B3%7D%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%281%29%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C%5Cxy%20+%20%5Cfrac%7By%7D%7Bz%7D%20=%208%5Cfrac%7Bx%7D%7Bz%7D%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%282%29%5C%5Cxy%20+%201%20=%20%5Cfrac%7B%7B9y%7D%7D%7B%7B2z%7D%7D%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%5C,%283%29%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />(Lấy (1)-(2) và (2)-(3) thu đc hệ dưới)<img src="https://latex.codecogs.com/gif.latex?%5CLeftrightarrow%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7D%5Cfrac%7Bx%7D%7Bz%7D%20-%20%5Cfrac%7By%7D%7Bz%7D%20=%20%5Cfrac%7B7%7D%7B3%7D%20-%20%5Cfrac%7B%7B8x%7D%7D%7Bz%7D%5C%5C%5Cfrac%7By%7D%7Bz%7D%20-%201%20=%20%5Cfrac%7B%7B8x%7D%7D%7Bz%7D%20-%20%5Cfrac%7B%7B9y%7D%7D%7B%7B2z%7D%7D%5C%5Cxyz%20+%20y%20=%208x%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /> <img src="https://latex.codecogs.com/gif.latex?%5CLeftrightarrow%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7D9%5Cfrac%7Bx%7D%7Bz%7D%20-%20%5Cfrac%7By%7D%7Bz%7D%20=%20%5Cfrac%7B7%7D%7B3%7D%5C%5C%5Cfrac%7B%7B11y%7D%7D%7B%7B2z%7D%7D%20-%201%20=%208%5Cfrac%7Bx%7D%7Bz%7D%5C%5Cxyz%20+%20y%20=%208x%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /> <img src="https://latex.codecogs.com/gif.latex?%5CLeftrightarrow%20%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7D%5Cfrac%7B%7B99x%7D%7D%7B2z%7D%20-%20%5Cfrac%7B%7B11y%7D%7D%7B%7B2z%7D%7D%20=%20%5Cfrac%7B%7B77%7D%7D%7B6%7D%5C%5C%5Cfrac%7B%7B11y%7D%7D%7B%7B2z%7D%7D%20-%201%20=%208%5Cfrac%7Bx%7D%7Bz%7D%5C%5Cxyz%20+%20y%20=%208x%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />(lấy pt thứ 1 +pt thứ 2 trong hệ <img src="https://latex.codecogs.com/gif.latex?%5CLeftrightarrow%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7D%5Cfrac%7By%7D%7Bz%7D%20=%20%5Cfrac%7B%7B9x%7D%7D%7Bz%7D%20-%20%5Cfrac%7B7%7D%7B3%7D%5C%5C%5Cfrac%7B%7B83%7D%7D%7B2%7D%5Cfrac%7Bx%7D%7Bz%7D%20=%20%5Cfrac%7B%7B83%7D%7D%7B6%7D%5C%5Cxyz%20+%20y%20=%208x%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /><img src="https://latex.codecogs.com/gif.latex?%20%5CLeftrightarrow%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7D%5Cfrac%7Bx%7D%7Bz%7D%20=%20%5Cfrac%7B1%7D%7B3%7D%5C%5C%5Cfrac%7By%7D%7Bz%7D%20=%20%5Cfrac%7B2%7D%7B3%7D%5C%5Cxyz%20+%20y%20=%208x%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /><img src="https://latex.codecogs.com/gif.latex?%20%5CLeftrightarrow%20%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7Dx%20=%20%5Cfrac%7Bz%7D%7B3%7D%5C%5Cy%20=%20%5Cfrac%7B%7B2z%7D%7D%7B3%7D%5C%5C%5Cfrac%7B2%7D%7B3%7D%7Bz%5E3%7D%20+%202z%20=%208z%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />Vì <img src="https://latex.codecogs.com/gif.latex?z%20%5Cneq%200" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /> nên hpt trên tương đương<img src="https://latex.codecogs.com/gif.latex?%20%5CLeftrightarrow%20%5Cleft[%20%5Cbegin%7Barray%7D%7Bl%7D%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7Dz%20=%20%20-%203%5C%5Cx%20=%20%20-%201%5C%5Cy%20=%20%20-%202%5Cend%7Barray%7D%20%5Cright.%5C%5C%5Cleft%5C%7B%20%5Cbegin%7Barray%7D%7Bl%7Dz%20=%203%5C%5Cx%20=%201%5C%5Cy%20=2%20%5Cend%7Barray%7D%20%5Cright.%5Cend%7Barray%7D%20%5Cright." alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" />Vậy....p/s: Trong hệ trên có thể đặt <img src="https://latex.codecogs.com/gif.latex?%5Cfrac%7Bx%7D%7Bz%7D=a" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /> và <img src="https://latex.codecogs.com/gif.latex?%5Cfrac%7By%7D%7Bz%7D=b" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /> để làm đỡ cồng kềnh hơn. <img src="https://diendantoanhoc.net/forum/style_emoticons/default/image004.gif" alt="" class="fr-fic fr-dii fr-draggable " data-size="" style="" /></blockquote>

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