Đáp án:
Giải thích các bước giải:
(x-7).(x+1)=0
\(\left[ \begin{array}{l}x-7=0\\x+1=0\end{array} \right.\)
\(\left[ \begin{array}{l}x=7\\x=-1\end{array} \right.\)
\(\left[ \begin{array}{l}x=0+7\\x=0-1\end{array} \right.\)
2
a,5.(-8).(-2).(-3)
= [5.(-8)].[(-2).(-3)]
= -40.6
=-240
b, 4.(-5).2+2.(-5)-20
= -20.2+(-10)-20
=-20.(-10+2)
=-20.(-8)
=-160
c, 27.(15-12)-15.(27-12)
= 27.3-27.(15-12)
=27.3-27.3
= 0