Bài 1 : Tính hợp lí :
a ) – 27 + 58 – 83 + 42
b ) ( – 41 + 85 ) – ( 59 – 25 )
c ) – ( – 59 + 94 ) + ( -194 – 59 )
Bài 2 : Tìm x , biết :
a ) x – 14 = – 18
b ) – 4 + x = – 10
c ) – 21 – x = – 15
d ) 15 – ( – 8 – x )= 21
e ) | x + 2 | = 3
g ) x ² = 100
h ) ( x + 2 ) ² = 64
i ) ( 4 – x ) ² = 25
k ) ( 5 – x ) ² – 1 = 80
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Đáp án:
Giải thích các bước giải:
Bài 1
a, -27+58-83+42 = (58+42)-(27+83) = 100 -110 = -10
b, (-41+85 ) – (59-25) = – 41 + 85 – 59 +25 = (85+25) – (41+59) =110 – 100 = 10
c, -(-59+94) + (-194 -59 )= 59 -94 -194 -59 = (59-59)-(94+194) = -288
Bài 2
a, x – 14 = -18 => x = -18+14 => x= -4
b, -4 +x = -10 => x = -10 -(-4) => x = -10 +4 => x= -6
c, -21 -x = -15 => x = -21 – (-15) => x= -21+15 => x= -7
d, 15- (-8-x) =21 => 15+8 +x =21 => 23+x = 21 => x = 21-23=-2
e, l x+2 l = 3 => x+2 = 3 hoặc x+2 =-3
=> x= 1 hoặc x = -5
g, x^2 =100 => x=10 hoặc x=-10
h, (x+2)^2 =64 => x+2 = 8 hoặc x+2 =-8 =>x =6 hoặc x=-10
i, (4-x)^2 = 25 =>4-x = 5 hoặc 4-x =-5 => x= -1 hoặc x =9
k, (5-x)^2 -1 =80 => (5-x)^2 = 81 =>5-x = 9 hoặc 5-x =-9 => x = -4 hoặc x =14
1)
a) -27 + 58 – 83 + 42
= (58 + 42) – (27 + 83)
= 100 – 100
= 0
b) (-41 + 85) – (59 – 25)
= -41 + 85 – 59 + 25
= (85 + 25) – (41 + 59)
= 110 – 100
= 10
c) – ( – 59 + 94 ) + ( -194 – 59 )
= 59 – 94 – 194 – 59
= (59 – 59) – (94 + 6 + 188)
= 0 – 288
= -288
2)
a) x – 14 = -18
x = -4
b) -4 + x = -10
x = -6
c) -21 – x = -15
x = -6
d) 15 – (-8 – x) = 21
(-8 – x) = -6
-8 – x = -6
x = -2
e) | x + 2 | = 3
=>\(\left[ \begin{array}{l}x+2=3\\x+2=-3\end{array} \right.\) => \(\left[ \begin{array}{l}x=1\\x=-5\end{array} \right.\)
g) $x^2$ = 100
x = √100
x = 10
h) (x + 2)² = 64
x + 2 = √64
=>\(\left[ \begin{array}{l}x+2=8\\x+2=-8\end{array} \right.\) =>\(\left[ \begin{array}{l}x=6\\x=-10\end{array} \right.\)
i) (4 – x)² = 25
4 – x = √25
=> \(\left[ \begin{array}{l}4-x=25\\4-x=-25\end{array} \right.\) =>\(\left[ \begin{array}{l}x=-21\\x=29\end{array} \right.\)
k) (5 – x)² – 1 = 80
(5 – x)² = 81
5 – x = √81
=> \(\left[ \begin{array}{l}5-x=9\\5-x=-9\end{array} \right.\) =>\(\left[ \begin{array}{l}x=-4\\x=-14\end{array} \right.\)