Toán Lớp 6: 255-5.[2.(21-3x)^4-122]=55 giúp với
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Toán Lớp 6: 255-5.[2.(21-3x)^4-122]=55 giúp với
Comments ( 2 )
=>5.[2.(21-3x)^4-122]=255-55
=>5.[2.(21-3x)^4-122]=200
=>2.(21-3x)^4-122=200:5
=>2.(21-3x)^4-122=40
=>2.(21-3x)^4=40+122
=>2.(21-3x)^4=162
=>(21-3x)^4=162:2
=>(21-3x)^4=81
=>(21-3x)^4=(+-3)^4
=>[(21-3x=3),(21-3x=-3):}
=>[(3x=21-3),(3x=21+3):}
=>[(3x=18),(3x=24):}
=>[(x=18:3),(x=24:3):}
=>[(x=6),(x=8):}
Vậy x\in{6;8}
5.[2.(21-3x)^4-122]=255-55
5.[2.(21-3x)^4-122]=200
2.(21-3x)^4-122=200:5
2.(21-3x)^4-122=40
2.(21-3x)^4=40+122
2.(21-3x)^4=162
(21-3x)^4=162:2
(21-3x)^4=81
(21-3x)^4=3^4
=>21-3x=pm3
=>\(\left[ \begin{array}{l}21-3x=3\\21-3x=-3\end{array} \right.\)
=>\(\left[ \begin{array}{l}3x=21-3\\3x=21-(-3)\end{array} \right.\)
=>\(\left[ \begin{array}{l}3x=18\\3x=24\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=18:3\\x=24:3\end{array} \right.\)
=>\(\left[ \begin{array}{l}x=6\\x=8\end{array} \right.\)
Vậy x={6;8}