Đáp án + Giải thích các bước giải:
Bài `1`:
a, `(3x - 1)^4 = 81`
` (3x - 1)^4 = 3^4 = (-3)^4`
⇒\(\left[ \begin{array}{l}3x - 1 = 3\\3x - 1 = -3\end{array} \right.\)
⇒\(\left[ \begin{array}{l}3x = 4\\3x = -2\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = \frac{4}{3}\\ x = -\frac{2}{3}\end{array} \right.\)
Vậy `x \in {4/3 ; -2/3}`
b, `3^(2x - 1) = 3^243`
`=> 2x - 1 = 243`
`2x = 243 + 1`
`2x = 244`
` x = 244 : 2`
` x = 122`
Vậy `x = 122`
Bài `2`:
`D = 2^4 + 4^4 + 6^4 + 8^4 + 10^4`
` = 1^4 . 2^4 + 2^2 . 2^4 + 2^4 . 3^4 + 2^4 . 4^4 + 2^4 . 5^4`
` = 2^4 . (1^4 + 2^4 + 3^4 + 4^4 + 5^4)`
` => 16 . 979`
` D = 15664`
