1 + 3 - 2 +7 = 4 - 2 +7
= 2 + +7
= 9
1 + 3 - 2 +7 = 4 - 2 +7
= 2 + +7
= 9
1+2+3+4+5+6+7+8+9-1-2-3-4-5-6-7-8-9*2+1+2+3+4+5+6+7+8+9=
1+2+3+4+5+6+7+8+9+1+2+3+4+5+6+7+8+9+1+2+3+4+5+6+7+8+9
Tính nhanh:
a)2+4+8+6+7+8+3+9+2+1;
b)3+2+4+9+7+1+8+6+3+5;
c)2+3+4+5+6+7+8+9+1+4.
Cho S = 7^1+7^3+7^5+...+7^99 chứng minh S chia hết cho 35 cho S =2^1+2^2+2^3+....+2^90 chứng minh S chia hết cho 21
1+1+1+1+1+1+2+5+10+4+7=
(1+9)+(2+8)+(3+7)+(4+6)+(5+5)+(10+0)=
Xx1+3=7
Tính nhẩm:
a. 1+1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9= ....?
b. 9-9+8-8+7-6+6-5+1-3+2+4+5+6-3-8=....?
1 x 2 = ?
1 x 2 x 3 = ?
1 x 2 x 3 x 4 = ?
1 x 2 x 3 x 4 x 5 = ?
1 x 2 x 3 x 4 x 5 x 6 = ?
1 x 2 x 3 x 4 x 5 x 6 x 7 = ?
1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 = ?
1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 = ?
1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 10 = ?
1+2+3+4+5+6+7+8+9+0+1+1+2+3+4+5+6+7+8+890+
1+2+3+4+5+6+7+8+9+1+2+3+4+5+6+7+8+9