Đáp án:
Bài 6:
a, `(x + 5)³ = -64`
` (x + 5)³ = (-4)³`
`⇒ x + 5 = -4`
` x = -4 - 5 = -9`
b, `(2x - 3)² = 9`
`(2x - 3)² = 3² = (-3)²`
⇒\(\left[ \begin{array}{l}2x - 3 = 3\\2x - 3 = - 3\end{array} \right.\)
⇒\(\left[ \begin{array}{l}2x = 6\\2x = 0\end{array} \right.\)
⇒ \(\left[ \begin{array}{l}x=3\\x=0\end{array} \right.\)
Vậy `x ∈{ 3 ; 0}`
Bài 7:
`M = (8^10 + 4^10)/(8^4 + 4^11)`
` = ( (2³)^10 + 4^10)/( (2³)^4 + 4^11)`
` =( 2^30 + 4^10)/(2^12 + 4^11)`
` = ( (2^2)^15 + 4^10)/( (2^2)^6 + 4^11)`
` = (4^15 + 4^10)/(4^6 + 4^11)`
` =( 4^10 . ( 4^5 + 1))/(4^6 . (4^5 + 1))`
` = (4^10)/(4^6)`
` = 4^4 = 256`
