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