Question

Nhang tay nhanh tay , lì xì ngay 

Tính S = 1.2 + 2.3 + .... + 49.50 ( KHÔNG LÀM LINH TINH )

Answer 1

bai toan nay kho qua 

Answer 2

Ta có :
S=1x2+2x3+3x4+...+49.50

 3S=1x2x3+2x3x3+...+… +49x50x3

=> 3S=1x2x(3-0)+2x3x(4-1)+...+49x50(51-48)

=> 3S=1x2x3-0+2x3x4-1x2x3+...+49x50x51-48x49x50

=> 3S=49x50x51

=> S=49x50x513

=> S=41650

Đáp số : 41650

Answer 3

3S=1.2.3+2.3.3+3.4.3+...+49.50.3

=1.2.3+2.3.(4-1)+3.4.(5-2)+...+48.49.(50-47)+49.50.(51-48)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+48.49.50-47.48.49+49.50.51-48.49.50

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...(47.48.49-47.48.49)-(48.49.50-48.49.50)+49.50.51

=0+0+...+0+0+49.50.51

=49.50.51

S=(49.50.51)/3

=41650

Đáp số:41650