Tính nhanh
a,1.2.3+2.3.4+...+2014.2015.2016
B,(7/9+1).(7/20+1)....(7/10800+1)
Tính nhanh:(7/9+1)(7/20+1)(7/33+1)....(7/10800+1)
tinh nhanh A=(7/9+1)(7/20+1)(7/33+1).....(7/10800+1)
tính nhanh ;A=(7/9+1)(7/20+1)(7/33+1)....(7/10800+1)
Tính:
\(C=\left(\frac{7}{9}+1\right)\left(\frac{7}{20}+1\right)\left(\frac{7}{33}+1\right)...\left(\frac{7}{10800}+1\right)\)
Tính nhanh:
C=\(\left(\frac{7}{9}+1\right)\left(\frac{7}{20}+1\right)\left(\frac{7}{33}+1\right).......\left(\frac{7}{10800}+1\right)\)
tính nhanh A= \(\left(\frac{7}{9}+1\right).\left(\frac{7}{20}+1\right).\left(\frac{7}{33}+1\right)....\left(\frac{7}{10800}+1\right)\)
Tính nhanh:
C=( \(\frac{7}{9}\)+ 1)( \(\frac{7}{20}\)+ 1)( \(\frac{7}{33}\)+ 1).....( \(\frac{7}{10800}\)+ 1).
\(C=\left(\frac{7}{9}+1\right)\left(\frac{7}{20}+1\right)\left(\frac{7}{33}+1\right)...\left(\frac{7}{10800}+1\right)\)
\(=\frac{16}{9}.\frac{27}{20}.\frac{40}{33}.....\frac{10807}{10800}\)
\(=\frac{2.8}{1.9}.\frac{3.9}{2.10}.\frac{4.10}{3.11}.....\frac{101.107}{100.108}\)
\(=\frac{2.3.4....101}{1.2.3....100}.\frac{8.9.10...107}{9.10.11...108}\)
\(=101.\frac{2}{27}\)\(=\frac{202}{27}\)
Tính : A=1.2.3+2.3.4+3.4.5+......+99.100.101
Ai vừa thi HSG 7 thành phố cho xin cái đề
11 tính nhanh
a. -37 + 54 + -70+ -163 + 246
b. -359+ 181+ -123+ 350+ -172
c.-69+ 53+ 46+ -94+-14+ 78
d. 13- 12+ 11+10- 9+ 8- 7- 6+ 5- 4+ 3+2- 1
a. -37 + 54 + -70+ -163 + 246
= ( 54 + 246) + (-37 - 163 ) - 70
= 300 -200 - 70 = 30
b. -359+ 181+ -123+ 350+ -172
=(-178)+227+(-172)
=49+(-172)
=-123
c.-69+ 53+ 46+ -94+-14+ 78
=(-16)+(-48)+64
=-64+64
=0
d. 13- 12+ 11+10- 9+ 8- 7- 6+ 5- 4+ 3+2- 1
= 13 - (13 - 1) + (13 - 2) + (13 - 3) - (13 - 4) + (13 - 5) - (13 - 6) - (13 - 7) + (13 - 8) - (13 - 9) + (13 - 10) + (13 - 11) - (13 - 12)
= 13 - 13 + 1 + 13 - 2 + 13 - 3 - 13 + 4 + 13 - 5 - 13 + 6 - 13 + 7 + 13 - 8 - 13 + 9 + 13 - 10 + 13 - 11 - 13 + 12
= (13 - 13 + 13 + 13 - 13 + 13 - 13 - 13 + 13 - 13 + 13 + 13 - 13) + (1 - 2 - 3 + 4 - 5 + 6 + 7 - 8 + 9 - 10 - 11 = 12)
= 13 + 0
= 13
a) \(-37+54+\left(-70\right)+\left(-163\right)+246\)
\(=\left(246+54\right)-\left(37+163\right)-70\)
\(=300-200-70\)
\(=100-70=30\)
b) \(-359+181+\left(-123\right)+350+\left(-172\right)\)
\(=-359+181-123+350-172\)
\(=\left(-359+350\right)+\left(181-172\right)-123\)
\(=-9+9-123\)
\(=-123\)
c) \(-69+53+46+\left(-94\right)+\left(-14\right)+78\)
\(=-69+53+46-94-14+78\)
\(=\left(-69+78\right)+\left(53-14\right)+\left(46-94\right)\)
\(=9+39-48\)
\(=48-48=0\)
d) \(13-12+11+10-9+8-7-6+5-4+3+2-1\)
\(=\left(13-12\right)+\left(11+10\right)-\left(9-8\right)-\left(7+6\right)+\left(5-4\right)+\left(3+2-1\right)\)
\(=1+21-1-13+1+5\)
\(=21-13+1+5\)
\(=8+1+5=9+5=14\)