Toán Lớp 7: (3|x|+5)/3=(3|y|-1)/5=(3-z)/7 vaf 2|x|+7|y|+3z=-14
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Toán Lớp 7: (3|x|+5)/3=(3|y|-1)/5=(3-z)/7 vaf 2|x|+7|y|+3z=-14
các bạn giúp mình với
Comments ( 1 )
Đặt : $\frac{3|x|+5}{3}$ = $\frac{3|y|-1}{5}$ = $\frac{3-z}{7}$ = k
⇒ | x | = $\frac{3k-5}{3}$ ⇒ 2 | x | = $\frac{6k-10}{3}$
⇒ | y | = $\frac{5k+1}{3}$ ⇒ 7 | y | = $\frac{35k+7}{3}$
⇒ z = 3 – 7 k ⇒ 3 z = 9 – 21 k
Vì 2 | x | + 7 | y | + 3 z = – 14 ⇒ 7$\frac{6k-10}{3}$ + $\frac{35k+7}{3}$ + ( 9 – 21 k ) = – 14
⇒ $\frac{(6k-10)+(35k+7)+(27-63k)}{3}$ = – 14
⇒ $\frac{-22k+24}{3}$ = – 14
⇒ 22 k + 24 = – 42
⇒ k = $\frac{-42-22}{22}$ = 3
⇒ | x | = $\frac{3.3-5}{3}$ = $\frac{4}{3}$ ⇒ x = – $\frac{4}{3}$ ; $\frac{4}{3}$
⇒ | y | = $\frac{5.3+1}{3}$ = $\frac{16}{3}$ ⇒ y = – $\frac{16}{3}$ ; $\frac{16}{3}$
⇒ z = 3 – 7 .3 = – 18 .