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a) ( 2017 - x ) : 3 = 345
<=> 2017 - x = 1035
<=> x = 2017 - 1035
<=> x = 982
b) 317 - ( 213 - x ) = 137
<=> 213 - x = 317 - 137
<=> 213 - x = 180
<=> x = 213 - 180
<=> x = 33
c) [ (2x + 51 ) - 97 ] . 3 = 72
<=> (2x + 51) - 97 = 24
<=> 2x + 51 = 121
<=> 2x = 70
<=> x = 35
d) x + 345 : 15 = 65
<=> x + 23 = 65
<=> x = 42
e) 12x + 24 =744
<=> 12x = 720
<=> x = 60
g) 12 (x + 24) = 744
<=> x + 24 = 62
<=> x = 38
a) (-12).(-12) = 12.12 = 144
b) (-137) (-15) = 137.15 = 2055.
1) a) (-12).12 = -(12.12) = -144
b) 137.(-15) = -(137.15) = - 2 055
2) 5.(-12) = -(5.12) = -60
215 + 43 - 15 - 23
= (215 - 15) + (43 - 23)
= 200 + 20
= 220
2022 - (122 + 2022) + (122 - 325)
= 2022 - 122 - 2022 + 122 - 325
= (2022 - 2022) - (122 - 122) - 325
= 0 - 0 - 325
= - 325
12.(-137) + 12.136
= 12.( -137 + 136)
= 12.(-1)
= - 12
a] -567 + 113 - 113567 - 2011
= -454 - 113567 - 2011
= -114021 - 2011= -116032
B] -137 x [52 + 47+1]
= -137 x 100
= -13700
C] 15 x [16 - 222] - 16 x [222 + 15]
= 15 x [-206] - 16 x 237
= -3090 - 3792
= -6882
h)\(\left(2x-1\right)\left(x-7\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}2x-1=0\\x-7=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=7\end{cases}}\)
g) \(x^2+2x=0\)
\(\Leftrightarrow x\left(x+2\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=0\\x+2=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=0\\x=-2\end{cases}}\)
\(\frac{3}{3.6.9}+\frac{3}{6.9.12}+\frac{3}{9.12.15}+\frac{3}{12.15.18}=\frac{3}{6}\left(\frac{6}{3.6.9}+\frac{6}{6.9.12}+\frac{6}{9.12.15}+\frac{6}{12.15.18}\right)\)
= \(\frac{1}{2}\left(\frac{1}{3.6}-\frac{1}{6.9}+\frac{1}{6.9}-\frac{1}{9.12}+\frac{1}{9.12}-\frac{1}{12.15}+\frac{1}{12.15}-\frac{1}{15.18}\right)\)
\(=\frac{1}{2}\left(\frac{1}{3.6}-\frac{1}{15.18}\right)=\frac{1}{2}.\frac{14}{270}=\frac{7}{270}\)
(-12) x (-12 ) = 144
(-137 ) x (-15 ) = 2055
HT nhoa