\(A=1.3+2.4+3.5+....+48.50\)
\(A=1.\left(1+2\right)+2.\left(3+1\right)+3.\left(4+1\right)+....+48.\left(49+1\right)\)
\(A=1.2+1+2.3+2+3.4+3+....+48.49+48\)
\(A\left(=1.2+2.3+...+48.49\right)+\left(1+2+...+48\right)\)
tự làm tiếp :))
p/s: ck iu :3
A=(48.50.51-1.3.0):3=.....