Tinh tong S= 12+22+32+42+..............+202 - (1+2+3+...........+20)
S=
tinh nhanh: 1+1/2(1+2)+1/3(1+2+3)+1/4(1+2+3+4)+...+1/10(1+2+3+...+20)
1) tinh nhanh
a) 85.127+5.127.3
b) 1/2 + 5/6 + 11/2 +19/20 + 29/30 + 41/42 + 55/56 + 71/72 + 89/90
3) tinh gia tri bieu thuc
a) A= 2^2 + 4^2 + 6^2+ ...+ 20^2
b) B= 1^2 + 2^2 + 3^2 +...+ 10^2
tinh : (1/19+2/18+3/17+...+18/2+19/1)/1/2+1/3+1/4+...+1/20
Tinh:
1/19 + 2/18 + 3/17 +...+ 18/2 + 19/1
1/2 + 1/3 + 1/4 +...+ 1/19 + 1/20
1, tinh
a, 31×72+ (-31) ×70-31×(-1)
b,[3 ×(-2)/(-8)]×(-7)-(-2)×(-5)
c,(-3)^2+ 3^2-(-2)^3×(-3)^0
d,(-2)×(-3)÷(-1)-(-3)×(-2) ÷ (-6)+(-2)
e,[20×2^4-12×2^3+48×2^2]÷(-8)
tinh A= 4+2^2+2^3+...+2^20
tinh hop li:
a) 1+2+3...+20
b)1+3+5+...+21
c)2+5+8+...+2018 +2021
d)1*2+2*3+3*4+...+15*16
e)1*2*3+2*3*4+3*4*5+... +13*14*!5
tinh 4+2^2+2^3+2^4+...+2^20