tinh nhanh
39.(19-13)-19.(39-13)
(42-69+17)-(42+17)
137.(-26)+26.137
-67.11
65.(-21)
1. = 13
2. = 346
3.= -69
4. = -2600
5. -2150
789 - 9 (72 -19 ) . 13 + (42 + 26 ) : 17
giúp tôi nha
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70=?
tính bằng cách thuận tiện nhất :
a) (3/13 x 17/29 ) x 29/34 = ??
b) 4/21 x 19/33 + 25/42 x 19/33 =??
a,=3/13.17/29.29/34
=3/13.1/2
=3/26
b,=(4/21+25/42).19/33
=11/14.19/33
=19/42
`a, = 3/13 xx (17/29 xx 29/34)`
`= 3/13 xx 1/2`
`= 3/26`.
`b, = 19/33(4/21 + 25/42)`
`= 19/33 xx ( 33/42 )`
`= 19/42`
`a)(3/13xx17/29)xx29/34=3/13xx17/29xx29/34=[3xx17xx29]/[13xx19xx17xx2]=3/26`
`b)4/21xx19/33+25/42xx19/33=19/33xx(4/21+25/42)=19/33xx(8/42+25/42)=19/33xx33/42=19/42`
12) 17 – 11 – 14 – (-39)
13) −127 - 18.( 5 - 6)
14) 100 + (+430) + 2145 + (-530)
15) (+12).13 + 13.(-22)
16) {[14 : (-2)] + 7} : 2012
17) 13 – 18 – (- 42) - 15
18) 369 – 4[(-5) + 4.(-8)]
19) (-12).(-13) +13.(-29)
20) 125 – 4[ 3 – 7.(-2) ]
21) (-14).9 – 13.(-9) chỉ em với
12) 17 – 11 – 14 – (-39)
=17-11-14+39
=6-14+39
=-8+39
=31
13) −127 - 18.( 5 - 6)
=-127-18.1
=-145
14) 100 + (+430) + 2145 + (-530)
=530+2145-530
=(530-530)+2145
=0+2145
=2145
15) (+12).13 + 13.(-22)
=13.[12+(-22)]
=13.(-10)
=-130
16) {[14 : (-2)] + 7} : 2012
={-7+7}:2012
=0:2012
=0
17) 13 – 18 – (- 42) - 15
=13-18+42-15
=-5+42-15
=37-15
=22
18) 369 – 4[(-5) + 4.(-8)]
=369-4[-5+(-32)]
=369-4(-37)
=369+148
=517
19) (-12).(-13) +13.(-29)
=12.13+13.(-29)=13.[12+(-29)]=13.(-17)=-221
20) 125 – 4[ 3 – 7.(-2) ]
=125-4[3+14]
=125-4.17
=125-68
=57
21) (-14).9 – 13.(-9)
=(-14).9+13.9
=9.[-14+13]
=9.(-1)
=-9
âm 9 nha bạn
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50=?
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50=1275
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50.
Có ai rảnh đâu mà đi ngồi cộng ngần đấy số ra.
2/6+9/20-11/30+13/42-15/56+17/72-19/90+21/110-23/132
Hôm nay olm.vn sẽ hướng dẫn các em giải dạng toán nâng cao cấu trúc thi hsg, violympic tính nhanh tổng các phân số mà tử số bằng tổng hai thừa số dưới mẫu:
Kiến thức cần nhớ: \(\dfrac{a}{b.c}\) trong đó a = b + c
+ Tách từng phân số thanh tổng hai phân số :
\(\dfrac{a}{b.c}\) = \(\dfrac{b+c}{b.c}\) = \(\dfrac{1}{b}+\dfrac{1}{c}\)
+ Triệt tiêu các hạng tử giống nhau.
+ Thu gọn ta được tổng cần tính
\(\dfrac{2}{6}+\dfrac{9}{20}-\dfrac{11}{30}+\dfrac{13}{42}-\dfrac{15}{56}+\dfrac{17}{72}-\dfrac{19}{90}+\dfrac{21}{110}-\dfrac{23}{132}\)
=\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)-(\(\dfrac{1}{5}+\dfrac{1}{6}\))+\(\dfrac{1}{6}\)+\(\dfrac{1}{7}\)-(\(\dfrac{1}{7}\)+\(\dfrac{1}{8}\))+\(\dfrac{1}{8}\) +\(\dfrac{1}{9}\)-(\(\dfrac{1}{9}\)+\(\dfrac{1}{10}\))+\(\dfrac{1}{10}\)+\(\dfrac{1}{11}\)-(\(\dfrac{1}{11}\)+\(\dfrac{1}{12}\))
= \(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)-\(\dfrac{1}{5}\)-\(\dfrac{1}{6}\)+\(\dfrac{1}{6}\)+\(\dfrac{1}{7}\)-\(\dfrac{1}{7}\)-\(\dfrac{1}{8}\)+\(\dfrac{1}{8}\)+\(\dfrac{1}{9}\)-\(\dfrac{1}{9}\)-\(\dfrac{1}{10}\)+\(\dfrac{1}{10}\)+\(\dfrac{1}{11}\)-\(\dfrac{1}{11}\)-\(\dfrac{1}{12}\)
= \(\dfrac{1}{3}\)+\(\dfrac{1}{4}\) - \(\dfrac{1}{12}\)
= \(\dfrac{4}{12}+\dfrac{3}{12}-\dfrac{1}{12}\)
= \(\dfrac{1}{2}\)
tính bằng cách thuận tiện nhất:
a) (3/13 x 17/29 ) x 29/34=
b) 4/21 x 19/33 x 25/42 x 19/33
gấp làm ơn