Đáp án:
`a, 5,5 + 4,5 - 5,5 +21,25 +7,75 - |-0,5|`
`= 5,5 + 4,5 - 5,5 +21,25 +7,75 - 0,5`
`=(5,5 + 4,5 ) - ( 5,5 + 0,5) + (21, 25 + 7,75)`
`= 10 - 6 + 29`
`= 33`
`b, (7x + 3)^4 = 625`
`<=> (7x + 3)^4 = (±5)^4`
`<=> 7x + 3 = -5 ; 5`
`<=> ` \(\left[ \begin{array}{l}7x+3=5\\7x+3=-5\end{array} \right.\)
`<=>` \(\left[ \begin{array}{l}7x=2\\7x=-8\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\frac{2}{7}\\x=\frac{-8}{7}\end{array} \right.\)
Vậy `S={ 2/7 ; -8/7}`