vi 1028 + 8 co tong cac chu so chia het cho 9 nen tong do chia het cho 9

ta co 1028 +8 co 3 chu so tan cung la 008 nen no chia het cho 8 

vay 1028 + 8 chia het cho 72

210 do nha ^_^

co len vong 16

Ta có :

\(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}=2\)

\(\Leftrightarrow\left(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}\right)^2=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+2.\dfrac{1}{a}.\dfrac{1}{b}+2.\dfrac{1}{b}.\dfrac{1}{c}+2.\dfrac{1}{a}.\dfrac{1}{c}=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+\dfrac{2}{ab}+\dfrac{2}{bc}+\dfrac{2}{ac}=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+\dfrac{2c}{abc}+\dfrac{2a}{abc}+\dfrac{2b}{abc}=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+\dfrac{2\left(a+b+c\right)}{abc}=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+\dfrac{2abc}{abc}=4\left(a+b+c=abc\right)\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}+2=4\)

\(\Leftrightarrow\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}=2\)

Vậy \(\dfrac{1}{a^2}+\dfrac{1}{b^2}+\dfrac{1}{c^2}=2\)

:D

sẽ bằng 2 giờ 24 phút 

số đó là:

28:7=4

    Đáp số: 4

> nha ban

ung ho mik ti nhe

đó chính là con cua

ai tk mình mình tk lại 

Bằng 20 bạn ơi !!!!

Ai tích mình mình tích lại cho!!!!!

44+56=100 nhé bạn