Toán Lớp 7: Tìm x biết:
a) x^7/81 = 27.
b) x^8/9 = 729.
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Toán Lớp 7: Tìm x biết:
a) x^7/81 = 27.
b) x^8/9 = 729.
Comments ( 2 )
⇒ x^7 : 81 = 27 .
⇒ x^7 = 27 \times 81.
⇒ x^7 = 3^3\times3^4.
⇒ x^7 = 3^7.
⇒ x = 3.
$\text{Vậy}$ x = 3.
⇒ x^8 : 9 = 729.
⇒ x^8 = 729 \times 9.
⇒ \(\left[ \begin{array}{l}x^8=3^2\times3^6.\\x^8=(-3)^2\times(-3)^6.\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x^8=3^8.\\x^8=(-3)^8.\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3.\\x=-3.\end{array} \right.\)
$\text{Vậy}$ x = 3 $\text{hoặc}$ x = -3.