Question

Cho biết 1^2+2^2+3^2+...+10^2=385, tính nhanh:

S=2^2+4^2+6^2+...+20^2. ;

P=3^2+6^2+9^2+...+30^2

Answer 1

\(S=2^2+4^2+....+20^2=?\)

\(=\left(2.1\right)^2+\left(2.2\right)^2+\left(2.3\right)^2+....+\left(2.10\right)^2\)

\(=2^2.1^2+2^2.2^2+2^2.2^3+...+2^2.10^2\)

\(=2^2.\left(1^2+2^2+3^2+...+10^2\right)\)

\(=2^2.385\)

\(=4.385\)

\(=1540\)

Answer 2

S=2²+4²+...+20²

=> 1/2 .S=1²+2²+...+10²

=> 1/2 .S=385

=> S = 385 . 2

=> S = 770

Answer 3

P=(1.3)²+...+(10.3)

   =3²(1²+...+10²)

   =9.385 = 3465

Answer 4

1540 ban nhe

Answer 5

1540 bạn

Answer 6

S=22+42+....+202=?

=(2.1)2+(2.2)2+(2.3)2+....+(2.10)2=(2.1)2+(2.2)2+(2.3)2+....+(2.10)2

=22.12+22.22+22.23+...+22.102=22.12+22.22+22.23+...+22.102

=22.(12+22+32+...+102)=22.(12+22+32+...+102)

=22.385=22.385

$=4.385$

$=1540$