=3²⁰ : 3¹⁵.(2³+1)
= 3⁵ . 9
=3⁵ . 3²
= 3⁷
 

(-1) + 2 + (-3) + 4 + ... + (-2019) + 2020

= [ (-1) + 2 ] + [ (-3) + 4 ] + ... + [ (-2019) + 2020 ]

= 1 + 1 + ... + 1

= 1 . 1010

= 1010

  (-1)+2+(-3)+4+...+(-2019)+2020

=(-1+2)+(-3+4)+...+(-2019+2020)

=1+1+...+1     (có 1010 số 1)

=1.1010

=1010

\(=\left(137-157\right)+\left(2020-40\right)=-20+1980=1960\)

số âm số dương

..................................................................

b: Sửa đề: \(B=1\cdot3+2\cdot4+3\cdot5+4\cdot6+\cdots+2018\cdot2020\)

\(=1\left(1+2\right)+2\left(2+2\right)+\cdots+2018\left(2018+2\right)\)

\(=\left(1^2+2^2+\cdots+2018^2\right)+2\left(1+2+\cdots+2018\right)\)

\(=\frac{2018\left(2018+1\right)\left(2\cdot2018+1\right)}{6}+2\cdot\frac{2018\cdot2019}{2}\)

\(=\frac{2018\cdot2019\cdot4037}{6}+2018\cdot2019=1009\cdot673\cdot4037+2018\cdot2019\)

\(=1009\cdot673\left(4037+2\cdot3\right)=1009\cdot673\cdot4043\)

=2745427451

c: Ta có: \(C=\left(1+2+3+\cdots+2020\right)\left(20192019\cdot2020-2019\cdot20202020\right)+\left(15-12\right)^2\)

\(=\frac{2020\left(2020+1\right)}{2}\cdot2019\cdot2020\cdot\left(10001-10001\right)+3^2\)

=0+9

=9

b: Sửa đề: \(B=1\cdot3+2\cdot4+3\cdot5+4\cdot6+\cdots+2018\cdot2020\)

\(=1\left(1+2\right)+2\left(2+2\right)+\cdots+2018\left(2018+2\right)\)

\(=\left(1^2+2^2+\cdots+2018^2\right)+2\left(1+2+\cdots+2018\right)\)

\(=\frac{2018\left(2018+1\right)\left(2\cdot2018+1\right)}{6}+2\cdot\frac{2018\cdot2019}{2}\)

\(=\frac{2018\cdot2019\cdot4037}{6}+2018\cdot2019=1009\cdot673\cdot4037+2018\cdot2019\)

\(=1009\cdot673\left(4037+2\cdot3\right)=1009\cdot673\cdot4043\)

=2745427451

c: Ta có: \(C=\left(1+2+3+\cdots+2020\right)\left(20192019\cdot2020-2019\cdot20202020\right)+\left(15-12\right)^2\)

\(=\frac{2020\left(2020+1\right)}{2}\cdot2019\cdot2020\cdot\left(10001-10001\right)+3^2\)

=0+9

=9

a: =-26+56=30

e: =-125+48+125-53=-5