Tinh nhanh:41.(14+5)+19.(43+16)
Tinh nhanh:41.(14+5)+19.(43+16)
\(41.\left(14+5\right)+19.\left(43+16\right)\)
\(=41.19+19.59\)
\(=19.\left(41+19\right)\)
\(=19.60=1140\)
Sorry mình viết nhầm,làm lại:
\(41.\left(14+5\right)+19.\left(43+16\right)\)
\(=41.19+19.59\)
\(=19.\left(41+59\right)\)
\(=19.100=1900\)
Cho A=4/7*31+6/7*41+9/10*41+7/10*57
B=7/19*31+5/19*43+3/23*43+11/23*57
Tinh ti so A/B
Ta có: \(A=\frac{4}{7.31}+\frac{6}{7.41}+\frac{9}{10.41}+\frac{7}{10.57}\)
\(=\frac{20}{35.31}+\frac{30}{35.41}+\frac{45}{50.41}+\frac{35}{50.57}\)
\(=5\left(\frac{4}{31.35}+\frac{6}{35.41}+\frac{9}{41.50}+\frac{7}{50.57}\right)\)
\(=5\left(\frac{1}{31}-\frac{1}{35}+\frac{1}{35}-\frac{1}{41}+\frac{1}{41}-\frac{1}{50}+\frac{1}{50}-\frac{1}{57}\right)\)
\(=5\left(\frac{1}{31}-\frac{1}{57}\right)\)
\(B=\frac{7}{19.31}+\frac{5}{19.43}+\frac{3}{23.43}+\frac{11}{23.57}\)
\(=\frac{14}{38.31}+\frac{10}{38.43}+\frac{6}{46.43}+\frac{22}{46.57}\)
\(=2\left(\frac{7}{31.38}+\frac{5}{38.43}+\frac{3}{43.46}+\frac{11}{46.57}\right)\)
\(=2\left(\frac{1}{31}-\frac{1}{38}+\frac{1}{38}-\frac{1}{43}+\frac{1}{43}-\frac{1}{46}+\frac{1}{46}-\frac{1}{57}\right)\)
\(=2\left(\frac{1}{31}-\frac{1}{57}\right)\)
\(\Rightarrow\frac{A}{B}=\frac{5\left(\frac{1}{31}-\frac{1}{57}\right)}{2\left(\frac{1}{31}-\frac{1}{57}\right)}=\frac{5}{2}\)
Thực hiện phép tính bằng cách hợp lí ( nếu có thể)
5/19- 19/5 + -27/43+ 14/19 + 16/-43
Thực hiện phép tính bằng cách hợp lí ( nếu có thể)
5/19- 19/5 + -27/43+ 14/19 + 16/-43
\(\frac{5}{19}-\frac{19}{5}-\frac{27}{43}+\frac{14}{19}-\frac{16}{43}\)
\(=\left(\frac{5}{19}+\frac{14}{19}\right)+\left(\frac{-27}{43}-\frac{16}{43}\right)-\frac{19}{5}\)
\(=1-1=0\)
tính 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+50-999-888-777-666-555-444-333-222-111
nhanh nhé
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+4
7+48+49+50-999-888-777-666-555-444-333-222-111= -3720
14+15+16+17+18+19 tinh nhanh nha
Olm sẽ hướng dẫn em cách làm như sau:
14 + 15 + 16 + 17 + 18 + 19
= (14 + 16) + (15 + 17 + 18) + 19
= 30 + 50 + 19
= 80 + 19
= 99
tinh nhanh
1+2+3+4+5+6+7+8+9+11+12+13+14+15+16+17+18+19
1+2+3+4+5+6+7+8+9+11+12+13+14+15+16+17+18+19
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)
=20+20+20+20+20+20+20+20+20
=20x9
=180
\(1+2+3+4+5+6+7+8+9+11+12+13+14+15+16+17+18+19\)
\(=\left(1+19\right)+\left(2+18\right)+\left(3+17\right)+\left(4+16\right)+\left(5+15\right)+\left(6+14\right)+\left(7+13\right)+\left(8+12\right)+\left(9+11\right)\)\(=20+20+20+20+20+20+20+20+20\)
\(=20\times9\)
\(=180\)
1+2+3+4+5+6+7+8+9+11+12+13+14+15+16+17+18+19
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)
=20+20+20+20+20+20+20+20+20
=20x9
=180
B1.Tìm A/B biết:
A=4/(7*31)+6/(7*41)+9/(10*41)+7/(10*57)
B=7/(19*31)+5/(19*43)+3/(23*43)+11/(23*57)
B2:CMR:
A=1/52+2/53+3/54+...+11/512 <1/16
33333333333333333333333333333333333'3333333333333
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