1+2+3+4+5+6........+49+48+47+46+45+44=???
Tính nhanh : 50- 49+48-47+46-45+44-43+....+4-3+2-1
50- 49+48-47+46-45+44-43+....+4-3+2-1
= 1 + 1 + 1+ 1 + ... + 1 + 1
= 1 x 25
= 25
50-49+48-47+46-45+...+4-3+2-1
= (50-49)+(48-47)+(46-45)+...+(4-3)+(2-1)(có 25 cặp số)
=1+1+1+1+1...+1
=1.25
=25
Cho A=\(\frac{1}{4}.\frac{3}{6}.\frac{5}{8}....\frac{43}{46}.\frac{45}{48}\) và B=\(\frac{2}{5}.\frac{4}{7}.\frac{6}{9}.....\frac{44}{47}.\frac{46}{49}\).So sánh A và B
99-97+95-93+91-89+...+7-5+3-1 = ?
50-49+48-47+46-45+...+4-6+2-1 = ?
x+1/49+x+2/48+x+3/47+x+4/46+x+5/45=-5
\(A=\frac{1}{4}.\frac{3}{6}.\frac{5}{8}....\frac{43}{46}.\frac{45}{48}\)
\(B=\frac{2}{5}.\frac{4}{7}.\frac{6}{9}....\frac{44}{47}.\frac{46}{49}\)
a) So sánh A và B
b) Chứng minh A<133
\(A=\frac{1}{4}.\frac{3}{6}.\frac{5}{8}....\frac{43}{46}.\frac{45}{48}\)
\(B=\frac{2}{5}.\frac{4}{7}.\frac{6}{9}....\frac{44}{47}.\frac{46}{49}\)
a) So sánh A và B
b) Chứng minh A<133
a)Ta có:A:B=\(\left(\frac{1}{4}.\frac{3}{6}.\frac{5}{8}....\frac{43}{46}.\frac{45}{48}\right):\left(\frac{2}{5}.\frac{4}{7}.\frac{6}{9}....\frac{44}{47}.\frac{46}{49}\right)=\frac{\left(1.3.5...45\right).\left(2.4.6...46\right)}{\left(4.6.8...48\right)\left(5.7.9...49\right)}=\frac{3.2}{47.48.49}
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.
Tính chuỗi các giá trị sau
a)1+3+5+7+...+45+47+49
b)2+4+6+8+...46+48+50
a.so so hang cua tong do la (49-1)/2+1=25
tong cac so hang do la (49+1)*25/2=625
b. lam tuong tu nhu cau a nha ban
a, Từ 1 đến 49 có: ( 49 - 1 ) : 2 + 1 = 25 ( số hạng )
1 + 3 + 5 + 7 + ... + 45 + 47 + 49
= ( 49 + 1 ) x 25 : 2
= 625
Từ 2 đến 50 có: ( 50 - 2 ) : 2 + 1 = 25 ( số hạng )
2 + 4 + ... + 50
= ( 50 + 2 ) x 25 : 2 = 650