13 355 - 9 324 = 4031

23 216 + 12 452 = 35668

1477 + 2 119 = 3596

62 102 - 23 701 = 38401

11-12+13-14+...+119-200=(11-12)+(13-14)+...+(119-200)=(-1)+(-1)+...+(-1)=(-1).95=-95

Mấy bài trong SGK đều có lời giải trên mạng mà !

\(B=3+3^2+3^3+...+3^{118}+3^{119}+3^{120}\\ =\left(3+3^2+3^3\right)+\left(3^4+3^5+3^6\right)+...+\left(3^{118}+3^{119}+3^{120}\right)\\ =3.\left(1+3+3^2\right)+3^4.\left(1+3+3^2\right)+...+3^{118}\left(1+3+3^2\right)\\ =\left(3+3^4+...+3^{118}\right).\left(1+3+3^2\right)\\ =\left(3+3^4+...+3^{118}\right).13⋮13\left(ĐPCM\right)\)

thanks

Bài 1 :

\(A=2+2^2+2^3+2^4+...+2^{118}+2^{119}+2^{120}\)

\(\Rightarrow A=2\left(1+2^{ }+2^2\right)+2^4\left(1+2^{ }+2^2\right)+...+2^{118}\left(1+2^{ }+2^2\right)\)

\(\Rightarrow A=2.7+2^4.7+...+2^{118}.7\)

\(\Rightarrow A=7.\left(2+2^4+...+2^{118}\right)⋮7\)

\(\Rightarrow dpcm\)

Bài 2 :

\(...=23\left(78+22\right)-15=23.100-15=2300-15=2285\)

ko bt bài 1

bài 2 là

=23.(78+22)-15

=23.100-15

=2300-15

=2275

hết

Bài 1 :

A = (2 + 2² + 2³) + (2⁴ + 2⁵ + 2⁶) + ... + (2¹¹⁸ + 2¹¹⁹ + 2¹²⁰)

A = 2.(1 + 2 + 4) + 2⁴.(1 + 2 + 4) + ... + 2¹¹⁸.(1 + 2 + 4)

A = 7.(2 + 2⁴ + ...  + 2¹¹⁸)   ⋮  7 (đfcm)