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\(a,\left(19x+2.5^2\right):14=\left(13-8\right)^2-4^2\)
\(\Leftrightarrow\left(19x+50\right):14=5^2-4^2\)
\(\Leftrightarrow\left(19x+50\right):14=9\)
\(\Leftrightarrow19x+50=126\)
\(\Leftrightarrow19x=76\Leftrightarrow x=4\)
b) x + ( x + 1 ) + ( x + 2 ) + ... + ( x + 30 ) = 1240
x + x + 1 + x + 2 + ... + x + 30 = 1240
( x + x + ... + x ) + ( 1 + 2 + ... + 30 ) = 1240
Số số hạng là : ( 30 - 1 ) : 1 + 1 = 30 ( số )
Tổng là : ( 30 + 1 ) . 30 : 2 = 465
=> 31x + 465 = 1240
=> 31x = 775
=> x = 25
Vậy........
a, (19x+2.52) : 14 = (13-8)2 - 42
(19x + 2.25) : 14 = 52 - 42
(19x + 50) : 14 = 25 - 16
(19x + 50) : 14 = 9
19 x + 50 = 9.14
19x + 50 = 126
19x = 126 - 50
19x = 76
x = 76 : 19
x = 4
vậy____
b) x + (x + 1) + (x + 2) + (x + 3)+.....+(x+30) = 1240
(x+x+x+...+x) + (1+2+3+...+30) = 1240
31x + 465 = 1240
31x = 1240 - 465
31x = 775
x = 775 : 31
x = 25
vậy____
c) |x + 7| = 20 + 5.(-3)
|x + 7| = 20 + (-15)
|x + 7| = 5
\(\Rightarrow\orbr{\begin{cases}x+7=5\\x+7=-5\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=5-7\\x=-5-7\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=-2\\x=-12\end{cases}}\)
vậy_____
a) \(\left(19x+2\cdot5^2\right):14=\left(13-8\right)^2-4^2\)
\(\Leftrightarrow\left(19x+2\cdot25\right):14=5^2-4^2\)
\(\Leftrightarrow19x+50=\left(25-16\right)\cdot14\)
\(\Leftrightarrow19x+50=9\cdot14\)
\(\Leftrightarrow19x+50=126-50\)
\(\Leftrightarrow19x=76\)
\(\Leftrightarrow x=76:19\)
\(\Leftrightarrow x=4\)
b) \(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\)
\(\Leftrightarrow\left(x+x+x+x...+x\right)+\left(1+2+3+...+30\right)=1240\)
\(\Leftrightarrow31x+\frac{\left[\left(30-1\right):1+1\right]\cdot\left(30+1\right)}{2}=1240\)
\(\Leftrightarrow31x+465=1240\)
\(\Leftrightarrow31x=775\)
\(\Leftrightarrow x=25\)
c)\(11-\left(-53+x\right)=97\)
\(\Leftrightarrow-53+x=-86\)
\(\Leftrightarrow x=-33\)
d) \(-\left(x+84\right)+213=-16\)
\(\Leftrightarrow-\left(x+84\right)=-229\)
\(\Leftrightarrow x+84=229\)
\(\Leftrightarrow x=145\)
\(a.-8:\left(4\dfrac{1}{5}x+\dfrac{3}{10}\right)=4\dfrac{4}{9}\)
\(4\dfrac{1}{5}x+\dfrac{3}{10}=\left(-8\right):4\dfrac{4}{9}\)
\(4\dfrac{1}{5}x+\dfrac{3}{10}=\dfrac{-9}{5}\)
\(4\dfrac{1}{5}x=\dfrac{-9}{5}-\dfrac{3}{10}\)
\(4\dfrac{1}{5}x=\dfrac{-21}{10}\)
\(x=\dfrac{-21}{10}:\dfrac{21}{5}\)
\(x=\dfrac{-1}{2}\)
Vay \(x=\dfrac{-1}{2}\).
\(b.4\dfrac{2}{3}-\left(\dfrac{3}{5}:x\right)=-20\%\)
\(\dfrac{14}{3}-\left(\dfrac{3}{5}:x\right)=\dfrac{-1}{5}\)
\(\dfrac{3}{5}:x=\dfrac{14}{3}-\dfrac{-1}{5}\)
\(\dfrac{3}{5}:x=\dfrac{73}{15}\)
\(x=\dfrac{3}{5}:\dfrac{73}{15}\)
\(x=\dfrac{9}{73}\)
Vay \(x=\dfrac{9}{73}\).
Câu c; d; e tương tự nhé.
a) \(2\left(x-5\right)-3\left(x+7\right)=14\)
\(\Leftrightarrow2x-10-3x-21=14\)
\(\Leftrightarrow-x-31=14\)
\(\Leftrightarrow-x=45\Leftrightarrow x=-45\)
b) \(5\left(x-6\right)-2\left(x+3\right)=12\)
\(\Leftrightarrow5x-30-2x-6=12\)
\(\Leftrightarrow3x-36=12\)
\(\Leftrightarrow3x=48\Leftrightarrow x=16\)
c) \(3\left(x-4\right)-\left(8-x\right)=12\)
\(\Leftrightarrow3x-12-8+x=12\)
\(\Leftrightarrow4x-20=12\)
\(\Leftrightarrow4x=32\Leftrightarrow x=8\)
d) \(-7\left(3x-5\right)+2\left(7x-14\right)=28\)
\(\Leftrightarrow-21x+35+14x-28=28\)
\(\Leftrightarrow-7x+35=0\Leftrightarrow x=5\)
Bài 2:
a)
S = 1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + ...... + 17 - 18
= (1-2-3+4) + (5-6-7+8)+...+(14-15-16+17)-18
= 0+0+...+0-18
= -18
b)
S = 942 - 2567 + 2563 - 1942
= (942 - 1942) + (-2567 + 2563)
= -1000 + ( -4)
= -1004
c)
S = 152- (374-1152) + (-65+374)
= 1152 - 374 + 1152 +(-65)+374
= (1152+1152) - (374+374) + (-65)
= 1489
\(\left(19x+2.5^1\right):14=\left(13-8\right)^2-4^2.\)
\(\left(19x+10\right):14=5^2-4^2\)
\(\left(19x:4\right)+\left(10:4\right)=25-16\)
\(\left(19x:4\right)+\frac{5}{2}=9\)
\(19x:4=9-\frac{5}{2}\)
\(19x:4=\frac{13}{2}\)
\(19x=\frac{13}{2}.4=26\)
\(x=\frac{26}{19}\)
c,11-(-53+x)=97
-53+x=11-97
-53+x= -86
x = -86-(-53)
x= -33