Tính nhanh
C=1-4+7-10+...+3001-3004
Tính nhanh
C=1-4+7-10+...+3001-3004
\(C=1-4+7-10+...+3001-3004\)
\(\Rightarrow C=\left(1-4\right)+\left(7-10\right)+...+\left(3001-3004\right)\)
\(\Rightarrow C=\left(-3\right)+\left(-3\right)+...+\left(-3\right)\)
Có 501 số -3
\(\Rightarrow C=\left(-3\right).501\)
\(\Rightarrow C=-1503\)
tính tổng sau:
B = 1-4+7-10+...+ 3001
So sánh
A= 2219*2221*2226-2218*2223*2225
B= 3004*2999*2997-3003*2996*3001
\(A=2219.2221.2226-2218.2223.2225\)
\(A=2219.(2223-2).2226-2218.2223.2225\)
\(A=2219.2223.2226-2.2219.2226-2218.2223.2225\)
\(A=2223.(2219.2216-2218.2225)-2.2219.2216\)
\(A=2223.\left\{(2218+1).(2215+1)-2218.2225\right\}-2.2219.2216\)
\(A=2223.(2218+2225+1)-2219.2226-2219.2226\)
\(A=2223.2219+2223.2225-2219.2226-2219.2226\)
\(A=(2223.2219-2219.2226)+2223.2225-2219.2225-2219\)
\(A=2219.(-3)+2225.4-2219\)
\(A=2219.(-4)+2225.4\)
\(A=4.(2225-2219)\)
\(A=4.6\)
\(A=24\)
\(B=3004.2999.2997-3003.2996.3001\)
\(B=3004.2999.(3001-4)-3003.2996.3001\)
\(B=(3003+1).2999.3001-3004.2999.4-3003.2996.3001\)
\(B=3003.(2996+3).3001+2999.3001-3004.2999.4-3003.2996.3001\)
\(B=3003.2996.3001+3.3003.3001-3.3004.2999+2999.3001-3004.2999-3003.2996.3001\)
\(B=3.(3003.3001-3004.2999)+2999.(3001-3004)\)
\(B=3.\left\{\left(3004-1\right).\left(2999+2\right)-3004.2999\right\}-3.2999\)
\(B=3.\left(3004.2999+2.3004-2999-2-3004.2999\right)-3.2999\)
\(B=3.(2.3003-2999)-3.2999\)
\(B=6.3003-6.2999\)
\(B=6.(3003-2999)\)
\(B=6.4\)
\(B=24\)
Mà \(A=24\) , \(B=24\)
\(\Rightarrow A=B\)
A=2219*(2223-2)*2226 - 2218*2223*2225
=2219*2223*2226 - 2*2219*2226 - 2218*2223*2225
=2223*(2219*2226 - 2218*2225) - 2*2219*2226
=2223*[(2218+1)*(2225+1) - 2218*2225] - 2*2219*2226
=2223*(2218+2215+1) - 2*2219*2226
=2223*2219+2223*2225 - 2219*2226 - 2219*2226
=(2223*2219 - 2219*2226) +2223*2225 - 2219*2225 - 2219
=2219*(-3) + 2225*4 - 2219
=2219*(-4) + 2225*4 = 4*(2225-2219) = 4*6 = 24
B=3004*2999*(3001-4) - 3003*2996*3001
=(3003+1)*2999*3001 - 3004*2999*4 - 3003*2996*3001
=3003*(2996+3)*3001 +2999*3001 - 3004*2999*4 - 3003*2996*3001
=3003*2996*3001+3*3003*3001 +2999*3001 - 3*3004*2999 - 3004*2999 - 3003*2996*3001
=3*(3003*3001 - 3004*2999) + 2999*(3001-3004)
=3*[(3004-1)*(2999+2) - 3004*2999] - 3*2999
=3*(3004*2999+2*3004 - 2999 - 2 - 3004*2999) - 3*2999
=3*(2*3003-2999) - 3*2999
=6*3003 - 6*2999 = 6*(3003-2999) = 6*4 = 24
===> A=B (=24)
tính
S1=1 -4 + 7 -10 - 2998 + 3001
1-4+7-10-2998+3001
=-3+7-10-2998+3001
=4-10-2998+3001
=-6-2998+3001
=-3004+3001
=3
so sánh A và B
A=2219*2221*2226-2218*2223*2225
B=3004*2999*2997-3003*2996*3001
a. A = 1-4+7-10+...+2995-2998+3001 = ?
\(A=1-4+7-10+...+2995-2998+3001\)
\(A=1+3+3+...+3+3\)
Từ 4\(\rightarrow\)3001 có: \(\left(3001-4\right):3+1=1000\)
Tổng từ \(1\)\(\rightarrow3001\): \(1+3.1000=3001\)
Vậy \(A=3001\)
Tính hợp lý:
h,6830+(-993)+170+(-5007)
i,3020+(-999)+20+(-3001)
l,1+(-3)+5+(-7)+9+(-11)
m,(-2)+4+(-6)+8+(-10)+12
tinh nhanh :s2= 1-4+7-10 +....-2998 + 3001
Tính nhanh: 1-4+7-0+...-2998+3001