\(A=1.2+2.3+3.4+4.5+...+59.60\)
\(\Rightarrow3A=1.2.3+2.3.\left(4-1\right)+...+59.60.\left(61-58\right)\)
\(\Rightarrow3A=1.2.3+2.3.4-1.2.3+...+59.60.61-58.59.60\)
\(\Rightarrow3A=59.60.61\)
\(\Rightarrow A=\frac{59.60.61}{3}\)
tính nhanh:
B=1+2+4+5+7+8+10+...+119+121+122
C=1.2+2.3+3.4+...+58.59+59.60
tinh tong A=1.2+2.3+3.4+4.5+5.6+...+2016.2017
-3/2.3-3/3.4-3/4.5-3/5.6-3/6.7
Tính nhanh :
1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + .... + 1/200.201
1.2+2.3+3.4+4.5+5.6+...+99.100=???
A= 12+2.3+3.4.4.5+5.6+6.7+7.8+8.9
B= 12+2.3+3.4+4.5+..................+53.54
C= 12.13+13.14 +14.15 +15.16+.............+207.208
a, 1313/1212:x=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6
a, 1313/1212:x=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6
Tính B= \(\dfrac{1}{3.4}\)-\(\dfrac{1}{4.5}\)-\(\dfrac{1}{5.6}\)-\(\dfrac{1}{6.7}\)-\(\dfrac{1}{7.8}\)-\(\dfrac{1}{8.9}\)-\(\dfrac{1}{9.10}\)