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1) Tính
a, 5 + (-5) = 0
b, 71 - 52 = 19
c, 28 + - (82) = -54
d, 45 + (-31) - 45 + (-30) = 45 + (-31) + (-45) + (-30) = [45 + (-45)] + [(-31) + (30)]
= 0 + (-1) = -1
2)Tìm x
a, x - 5 = -15
x = (-15) + 5
x = -10
b, 21 + x = -79
x = (-79) - 21
x = -100
c, x - 15 = -23 + (-6)
x - 15 = -29
x = -29 + 15
x = -14
d, 200 - x = /-32/ - 41
200 - x = 32 - 41
200 - x = -9
x = 200 - (-9)
x = 209
1 Tính :
a)5+(-5)=0
b)71-52=19
c)28+(-82)=-54
d)47+(-30)=17
e)(-41)+(-59)=-100
f)75+(-10)=65
t)26-43=-17
y)90-25=65
o)72+(-9)=63
p)(-3)+3=0
2 Tính nhanh :
a)(-150)-47+150-53
=(-150+150)+(-47-53)
=-100
b)250+(-90)-250-10+100
=(250-250)+(90-10)-250
=0-100-250=-350
c)71+92-28-(-29)+8-72
=71+92-28+29+8+72
=(71+29)+(92+8)+(72-28)
=100+100-44=156
d)45+(-31)-45+(-31)
=(45-45)+(-31-31)
=-62
a) 5 + (-5) = 0
b) 71-52 = 19
c) 28 + (-82) = -64
d) 47 + (-30) = 17
e) (-41) + (-59) = -100
f) 75 + (-10) = 65
t) 26 - 43 = -17
y) 90 - 25 = 650
o) 72 + (-9) = 63
p) (-3) + 3 = 0
\(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)
\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=8-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)
\(=\frac{38}{5}\)
a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{6}+1-\frac{1}{12}+...+1-\frac{1}{90}\)
\(=\left(1+1+1+...+1\right)-\left(\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\right)\)
\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{9\cdot10}\right)\)
Từ 2 đến 9 có : ( 9 - 2 ) / 1 + 1 = 8 ( số hạng ) => có 8 số 1
\(\Rightarrow8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)\)
\(=8-\frac{2}{5}=\frac{38}{5}\)
b) \(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+...+\frac{109}{110}\)
\(=1-\frac{1}{2}+1-\frac{1}{6}+...+1-\frac{1}{110}\)
\(=\left(1+1+1+...+1\right)-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{110}\right)\)
\(=\left(1+1+...+1\right)-\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+...+\frac{1}{10\cdot11}\right)\)
Từ 1 đến 10 có : ( 10 - 1 ) / 1 + 1 = 10 ( số hạng ) => có 10 số 1
\(\Rightarrow10-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{10}-\frac{1}{11}\right)\)
\(=10-\left(1-\frac{1}{11}\right)\)
\(=10-\frac{10}{11}=\frac{100}{11}\)
a) \(\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+\frac{29}{30}+\frac{41}{42}+\frac{55}{56}+\frac{71}{72}+\frac{89}{90}\)
\(=1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+1-\frac{1}{30}+1-\frac{1}{42}+1-\frac{1}{56}+1-\frac{1}{72}+1-\frac{1}{90}\)
\(=8-\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)\)
\(=8-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(=8-\left(\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+\frac{8-7}{7.8}+\frac{9-8}{8.9}+\frac{10-9}{9.10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
\(=8-\left(\frac{1}{2}-\frac{1}{10}\right)=7,6\)
b) Bạn làm tương tự.
\(y=\frac{1+5+11+19+29+41+55+71+89}{2+6+12+20+30+42+56+72+90}\)
\(y=\frac{1x2-1+2x3-1+3x4-1+4x5-1+5x6-1+6x7-1+7x8-1+8x9-1+9x10-1}{1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9+9x10}\)
\(y=\frac{\left(1x2+2x3+...+9x10\right)-\left(1+1+1+1+1+1+1+1+1\right)}{1x2+2x3+...+9x10}\)
\(y=\frac{1x2+2x3+...+9x10}{1x2+2x3+...+9x10}-\frac{9}{1x2+2x3+...+9x10}\)
\(y=1-\frac{9}{1x2+2x3+...+9x10}\)
vì bài dài nên mk chỉ ghi kết quả thui nha
a,0
b,19
c,-54
d,17
e,-100
f,65
t,17
y,65
o,63
p,0
3,
a,-10
b,-100
1 Tính :
a)5+(-5)=0
b)71-25=46
c)28+(-82)=-54
d)47+(-30)=17
e)(-41)+(-59)=-100
f)75+(-10)=65
t)26-43=-17
y)90-25=65
o)72+(-9)=63
p)(-3)+3=0
2 Tính nhanh :
a)(-150)-47+150-53
=(-150+150)-47-53
=-100
b)250+(-90)-250-10+100
=(250-250)+(-90)-10+100
=0
c)71+92-28-(-29)+8-72
=71+92-28+29+8-72
=(71+29)+(92+8)-(28+72)
=100+100-100
=100
d)45+(-31)-45+(-31)
=(45-45)+(-31+-31)
=-62
3 Tìm x biết :
a)x-5=-15
x=-15+5
x=-10
b)21+x=-79
x=-79-21
x=-100
c)x-15=-23+(-6)
x-15=-29
x=-29+15
x=-14
d)200-x=/-32/-41
200-x=32-41
200-x=-9
-x=-9-200
-x=-209
=>x=209