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2/(11x13) = 1/11 - 1/13 ; 2/(13x15) = 1/13 - 1/15 ; 2/(15x17) = 1/15 - 1/17 ; 2/(17x19) = 1/17 - 1/19 ; 2/(19x21) = 1/19 - 1/21
2/(11x13) + 2/(13x15) + 2/(15x17) + 2/(17x19) 2/(19x21) =
1/11 - 1/13 + 1/13 - 1/15 + 1/15 - 1/17 + 1/17 - 1/19 + 1/19 - 1/21 = 1/11 - 1/21 = 101231
Hay: 10/231 x 462 - X = 19
20 - X = 19
X = 20 - 19
X = 1,đó là phần b
1/3x + 3/4x - 75% = -5 1/4
=> x - 3/4 = -21/4
=> x = -21/4 + 3/4
=> x = -9/2
60%x + 5/6x = -76
=> 3/5x + 5/6x = -76
=> 43/30x = -76
=> x = -76 : 43/30
=> x = -2280/43
\(\frac{1}{3}x+\frac{3}{4}x-75\%=-5\frac{1}{4}\)
\(\frac{13}{12}x-\frac{3}{4}=-\frac{21}{4}\)
\(\frac{13}{12}x=-\frac{9}{2}\)
\(x=-\frac{54}{13}\)
\(60\%.x+\frac{2}{3}x=-76\)
\(\frac{3}{5}x+\frac{2}{3}x=-76\)
\(\frac{19}{15}x=-76\)
\(x=-60\)
\(3\left(x+2\right)+2x=76\)
\(3x+6+2x=76\)
\(3x+2x+6=76\)
\(5x=76-6\)
\(\Rightarrow5x=70\)
\(\Rightarrow x=70:5\)
\(\Rightarrow x=14\)
a, 55 - x + 33 = 76
=> - x = 76 - 55 - 33
=> - x = - 12
=> x = 12
vậy_
b, (x + 1) + (x + 2) + (x + 3) +.......+ (x + 100) = 5550
=> x + 1 + x + 2 + x + 3 + ... + x + 100 = 5550
=> (x + x + x + ... + x) + (1 + 2 + 3 + ... + 100) = 5550
=> 100x + 5050 = 5550
=> 100x = 500
=> x = 5
vậy_
Giải cho bạn 2 bài tìm x nhé! Bài kia dễ,tự giải
a) \(3^{x+2}-3^x=8.243\Leftrightarrow3^x.3^2-3^x=1944\)
\(\Leftrightarrow3^x\left(3^2-1\right)=1944\Leftrightarrow3^x.8=1944\)
\(\Leftrightarrow3^x=243=3^5\Leftrightarrow x=5\)
b) \(1+2+3+...+x=210\)
\(\Leftrightarrow\frac{x\left(x+1\right)}{2}=210\Leftrightarrow x\left(x+1\right)=420\)
\(\Leftrightarrow20\left(20+1\right)=420\Rightarrow x=20\)
Bài 1:
\(101\cdot125+101\cdot25-101\cdot50\)
\(=101\cdot\left(125+25-50\right)\)
\(=101\cdot100\)
\(=10100\)
Bài 2:
\(76\cdot115+56\cdot24+59\cdot24\)
\(=76\cdot115+24\cdot\left(56+59\right)\)
\(=76\cdot115+24\cdot115\)
\(=115\cdot\left(76+24\right)\)
\(=115\cdot100\)
\(=11500\)
\(60\%x+\dfrac{2}{3}x=-76\)
\(\Leftrightarrow\dfrac{3}{5}x+\dfrac{2}{3}x=-76\)
\(\Leftrightarrow\dfrac{19}{15}x=-76\)
\(\Leftrightarrow x=\dfrac{-76}{\dfrac{19}{15}}\)
\(\Leftrightarrow x=-60\)
\(60\%.x+\dfrac{2}{3}.x=-76\\ \dfrac{3}{5}.x+\dfrac{2}{3}.x=-76\\ \dfrac{19}{15}.x=-76\\ x=-76:\dfrac{19}{15}\\ x=-60.\)