Question

tính tổng A = 1.2+2.3+3.4+...+150.151

Answer 1

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

\(S=\frac{\left(49.50.51\right)}{3}\)

=41650

Đáp số:41650

Answer 2

3A=1.2.3+2.3.3+..............+150.151.3

=1.2.3+2.3.(4-1)................+150.151.(152-149)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+....................+150.151.152-149.150.151

=150.151.152

=>A=\(\frac{150.151.152}{3}\)

A=1147600

thấy ổn thì t nhé