(-12)+(-23)+(-42)
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Sửa đề: \(2x+\dfrac{11}{6}+\dfrac{23}{12}+\dfrac{39}{20}+\dfrac{59}{30}+\dfrac{83}{42}+\dfrac{111}{56}=12\)
\(\Leftrightarrow2x+\left(2+2+2+2+2+2\right)-\left(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\right)=12\)
\(\Leftrightarrow2x-\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{7}-\dfrac{1}{8}\right)=0\)
\(\Leftrightarrow2x-\dfrac{3}{8}=0\)
hay x=3/16


e. = 12 - 25 + 38 + 25 - 38 + 88 - 250
= ( -25 + 25) + (38 - 38) + ( 12 + 88) - 250
= -150
f. = (-12).44 + 44.(-88)
= 44 ( -12 -88 )
= 44 . 100
= 4400
g. = -48 + 54 -77 -24 + 48 + 77
= (-48 + 48) + (-77+77) + (54 -24)
= 30
h. = 11.(-42) + 11.(-26) + 42.11 + 42.26 -26.11 - 42.26
= \([11.\left(-42\right)+11.42]+\left[11.\left(-26\right)-26.11\right]+[42.26-42.26]\)
= 11. (-52)
= - 572
\(e.-\left(-12+25-38\right)+\left(25-38+88\right)-250\\ =12-25+38+25-38+88-250\\ =\left(25-25\right)+\left(38-38\right)+\left(12+88\right)-250\\ =0+0+100-250=-150\)
\(f.\left(-12\right)\cdot\left(67-23\right)+44\cdot\left(-88\right)\\ =\left(-12\right)\cdot44+44\cdot\left(-88\right)\\ =44\cdot\left[-12+\left(-88\right)\right]\\ =44\cdot\left(-100\right)=-4400\)
\(g.\left(-48+54-77\right)-\left(24-48-77\right)\\ =-48+54-77-24+48+77\\ =\left(48-48\right)+\left(54-24\right)+\left(77-77\right)\\ =0+30+0=30\)
\(h.11\cdot\left(-42-26\right)+42\cdot\left(11+26\right)-26\cdot11-42\cdot26\\ =11\cdot\left(-68\right)+42\cdot37-26\cdot11-42\cdot26\\ =-748+1554-286-1092=-572\)

a. (15+37)+(52-37-17) = 15+37+52-37-17
= 15+(37-37)+52-17
= 15+0+35
= 50

\(\left(2^{17}+7^2\right).\left(9^{15}-3^{15}\right).\left(2^4-4^2\right)\)
\(=\left(2^{17}+7^2\right).\left(9^{15}-3^{15}\right).\left(16-16\right)\)
\(=\left(2^{17}+7^2\right).\left(9^{15}-3^{15}\right).0\)
\(=0\)
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\(\left(7^{1997}-7^{1995}\right):\left(7^{1994}.7\right)\)
\(=\left[7^{1995}\left(7^2-1\right)\right]:7^{1995}\)
\(=7^{1995}.48:7^{1995}\)
\(=48\)
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\(\left(1^2+2^3+3^4+4^5\right).\left(1^3+2^3+3^3+4^3\right).\left(3^8-81^2\right)\)
\(=\left(1^2+2^3+3^4+4^5\right).\left(1^3+2^3+3^3+4^3\right).\left(6561-6561\right)\)
\(=\left(1^2+2^3+3^4+4^5\right).\left(1^3+2^3+3^3+4^3\right).0\)
\(=0\)
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\(\left(2^8+8^3\right):\left(2^5.2^3\right)\)
\(=\left[2^8+\left(2^3\right)^3\right]:2^8\)
\(=\left(2^8+2^9\right):2^8\)
\(=2^8.\left(1+2\right):2^8\)
\(=2^8.3:2^8\)
\(=3\)
