Bài 1 Tính hợp lí nếu có thể :
a ) 73 – ( 173 – 21 ) b ) – ( – 121 + 43 ) – 21
c ) ( – 35 + 79 ) – ( 165 – 21 ) d ) 47 . 63 + 47 . ( – 163 )
e ) ( – 25 ) . 39 + 61 . ( – 25 ) g ) 43 . 84 – 43 . 184
h ) 56 . ( – 27 ) + 27 . ( – 44 ) i ) 125 . 48 + ( – 125 ) . 56
Bài 2 : Tìm x , biết :
a ) – x + 13 = – 12 b ) – x – 19 = 40 c ) – 31 + x = – 15
d ) 13 + x = – 20 e ) – 21 – x = – 33 f ) 13 + ( x – 40 ) = – 5
g ) – 24 – ( x – 12 ) = – 6 h ) 3x – 17 = x -3 m ) ( x – 3 ) ² = 25
NHANH Ạ , EM ĐANG CẦN GẤP Ạ
THANK YOU VERY MUCH
NGUYENTHITET
Đáp án:
Giải thích các bước giải:
Bài 1:Tính hợp lí nếu có thể :
a ) 73 – ( 173 – 21 )
= 73 – 173 + 21
= (73 – 173) + 21
= (-100) + 21
=(-79)
b ) – ( – 121 + 43 ) – 21
= 121 – 43 – 21
= (121 – 21) – 43
= 100 – 43
=57
c ) ( – 35 + 79 ) – ( 165 – 21 )
= – 35 + 79 – 165 + 21
= (- 35 – 165) + (79 + 21)
= (-200) + 100
=(-100)
d ) 47 . 63 + 47 . ( – 163 )
=47 . [63 + (-163)]
=47 . (63 – 163)
=47 . (- 100)
=(-4700)
e ) ( – 25 ) . 39 + 61 . ( – 25 )
=(-25) . (39 + 61)
=(-25) . 100
=(-2500)
g ) 43 . 84 – 43 . 184
=43 . (84 – 184)
=43 . (-100)
=(-4300)
h ) 56 . ( – 27 ) + 27 . ( – 44 )
=56 . ( – 1 ) . 27 + 27 . ( – 44 )
=( – 56 ) . 27 + 27 . ( – 44 )
=27 . [( – 56 ) + ( – 44 )]
= 27 . ( – 56 – 44 )
= 27 . ( – 100 )
=( – 2700 )
i ) 125 . 48 + ( – 125 ) . 56
=125 . 48 + 125 . ( – 1 ) . 56
=125 . 48 + 125 . ( -56 )
=125 . [48 + (-56)]
=125 . (48 – 56)
=125 . (- 8)
=(-1000)
Bài 2 : Tìm x , biết :
a ) – x + 13 = – 12
⇔- x = – 12 – 13
⇔- x = – 25
⇔ x = 25
Vậy x=25
b ) – x – 19 = 40
⇔- x = 40 + 19
⇔- x = 59
⇔ x = -59
Vậy x=(-59)
c ) – 31 + x = – 15
⇔ x = – 15 + 31
⇔ x = 16
Vậy x=16
d ) 13 + x = – 20
⇔ x = – 20 – 13
⇔ x = -33
Vậy x=(-33)
e ) – 21 – x = – 33
⇔ -x = – 33 + 21
⇔ -x = -12
⇔ x = 12
Vậy x=12
f ) 13 + ( x – 40 ) = – 5
⇔13 + x – 40 = – 5
⇔ x – 27 = – 5
⇔ x = – 5 + 27
⇔ x = 22
Vậy x=22
g ) – 24 – ( x – 12 ) = – 6
⇔- 24 – x + 12 = – 6
⇔- 12 – x = – 6
⇔ x = (-12) – (-6)
⇔ x = (-12) + 6
⇔ x = (-6)
Vậy x=(-6)
h ) 3x – 17 = x – 3
⇔3x – 17 – x + 3=0
⇔2x – 14 =0
⇔2x =14
⇔ x =14 : 2
⇔ x =7
Vậy x=7
m ) ( x – 3 )² = 25
⇔( x – 3 )² = (±5)²
⇔\(\left[ \begin{array}{l}x-3=5\\x-3=-5\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=5+3\\x=-5+3\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=8\\x=-2\end{array} \right.\)
Vậy x ∈ {8;-2}
Đáp án:
Giải thích các bước giải:
Bài 1 Tính hợp lí nếu có thể :
a ) 73 – ( 173 – 21 )
=73 – ( 100+73 – 21 )
=73 – 100-73 +21
=(73-73) – 100 +21
=0 -100 +21
=-100+21
=-79
b ) – ( – 121 + 43 ) – 21
= – ( – 100-21 + 43 ) – 21
= 100+21 – 43 – 21
=(21-21) +100-43
=0 +100-43
=100-43
=57
c ) ( – 35 + 79 ) – ( 165 – 21 )
= – 35 + 79 – 165 + 21
= (79+ 21) +(- 165 – 35)
= 100 + (-200)
=-100
d ) 47 . 63 + 47 . ( – 163 )
=47. (63-163)
=47. (-100)
=-4700
e ) ( – 25 ) . 39 + 61 . ( – 25 )
=(-25). (39+61)
=(-25). 100
=-2500
g ) 43 . 84 – 43 . 184
= 43 . ( 84 – 184)
=43 . ( -100)
=-4300
h ) 56 . ( – 27 ) + 27 . ( – 44 )
=(-27). (56+44)
=(-27). 100
=-2700
i ) 125 . 48 + ( – 125 ) . 56
= 125. 8.6 + ( – 125) . 7.8
=(125.8) . (6-7)
=1000 . (-1)
=-1000
Bài 2 : Tìm x , biết :
a ) – x + 13 = – 12
-x = (-12)-13
-x =-25
x =25
b ) – x – 19 = 40
-x=40+19
-x=59
x=-59
c ) – 31 + x = – 15
x= (-15)-(-31)
x=16
d ) 13 + x = – 20
x=(-20)-13
x=-33
e ) – 21 – x = – 33
x=(-21)-(-33)
x=12
f ) 13 + ( x – 40 ) = – 5
x – 40 =(-5)+(-13)
x – 40=-18
x=(-18)+40
x=22
g ) – 24 – ( x – 12 ) = – 6
( x – 12 )=(-24)-(-6)
( x – 12 )=-18
x=(-18)+12
x=-6
h ) 3x – 17 = x -3
⇔ 3x-x=17-3
2x =14
x=14:2
x=7
m ) ( x – 3 ) ² = 25
⇔ ( x – 3 ) ² =( ±5)²
⇒ x – 3 = 5 hoặc x – 3 = -5
x=5+3 x =(-5)+3
x=8 x =-2