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a: \(72\cdot56+56\cdot28=56\left(72+28\right)=5600\)
b: \(53\cdot125-24\cdot53-53=53\left(125-24-1\right)=5300\)
c: \(42\cdot53+47\cdot156-47\cdot114=42\cdot53+47\cdot42=4200\)
d: \(28\cdot76+28\cdot25+28=28\cdot\left(76+25+1\right)=2800\)
e: \(37\cdot59-37\cdot3+37\cdot49=37\left(59-3+49\right)=3885\)
a, \(3\left(2x+1\right)^2-2\left(x-5\right)^2+\left(x-1\right)\left(x+2\right)\)
\(=3\left(4x^2+4x+1\right)-2\left(x^2-10x+25\right)+x^2+x-2\)
\(=12x^2+12x+3-2x^2+20x-50+x^2+x-2\)
\(=11x^2+33x-49\)
\(3\left(2x+1\right)^2-2\left(x-5\right)^2+\left(x-1\right)\left(x+2\right)\)
\(=3\left(4x^2+4x+1\right)-2\left(x^2-10x+10\right)+x^2+2x-x-2\)
\(=12x^2+12x+3-2x^2-20x-20+x^2+2x-x-2\)
\(=11x^2+33x-15\)
A)25%-1 1/3+0,5.12/5 =1/4-4/3+1/2.12/5=3/12-16/12+6/5=-13/12+6/5=7/60 8x=7,8.x+25. 8x-7,8x=25. 0,2x=25. x=25:0,2. x=125
a) 215+(-38)-(-58)+9-85
=215-38+58+9-85
=(215-38)+(58+9)-85
=177+67-85
=159
b)(1267-196)-(267-304)
=1071-(-37)
=1108
c)(3965-2378)-(437-1378)-528
=1578-(-941)-528
=2000.
Con d mk chiu.
a) 215 + (-38) - (-58) + 9-85
=215 - 38 + 58 + 9 - 85
=(215 - 38) + (58 + 9) - 85
=177 + 67 - 85
=159
b)(1267 - 196) - (267 - 304)
=1071 - (-37)
=1108
c)(3965 - 2378) - (437 - 1378) - 528
=1578 - (-941) - 528
=2000
Bài 1:
\(\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+....+\frac{1}{8}.\frac{1}{9}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{8.9}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{2}-\frac{1}{9}=\frac{7}{18}\)
\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+1\right):2}=1\frac{2016}{2017}\)
\(\Rightarrow\frac{1}{2}\left(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}\right)=\frac{1}{2}.\frac{4033}{2017}\)
\(\Leftrightarrow\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x\left(x+1\right)}=\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x\left(x+1\right)}=\frac{4033}{4034}\)
\(\Rightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{4033}{4034}\)
\(\Rightarrow1-\frac{1}{x+1}=\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{x+1}=1-\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{x+1}=\frac{1}{4034}\)
\(\Rightarrow x+1=4034\)
\(\Rightarrow x=4034-1\)
\(\Rightarrow x=4033\)
\(a,\frac{3}{-56}-\frac{-7}{64}=\frac{-3.8}{448}+\frac{7.7}{448}=\frac{25}{448}\)
\(b,\frac{-5}{54}-\frac{11}{-36}=-\frac{5}{54}+\frac{11}{36}=\frac{-5.2}{108}+\frac{3.11}{108}=\frac{23}{108}\)
\(c,\frac{9}{28}+\frac{-2}{29}=\frac{9.29-2.28}{812}=\frac{205}{812}\)
\(d,\frac{-5}{-72}+\frac{7}{-48}=\frac{5}{72}-\frac{7}{48}=\frac{5.2-7.3}{144}=-\frac{11}{144}\)
\(e,\frac{-5y}{2x^3}+\frac{2x}{3y}=\frac{-5y.3y+2x.2x^3}{6x^3y}=\frac{-15y^2+4x^4}{6x^3y}\)
\(f,\frac{2}{3x^4y^5}+\frac{5y^3}{2x^6}=\frac{2.2x^2+5y^3.3y^5}{6x^6y^5}=\frac{4x^2+15y^8}{6x^6y^5}\)