Question

Tính nhanh : `81^2+69^2-19^2-31^2`

Answer 1

\(=\left(81-31\right)\left(81+31\right)+\left(69-19\right)\left(69+19\right)\\ =50\cdot112+50\cdot88=50\left(112+88\right)=50\cdot200=10000\)

Answer 2

\(=\left(81^2-31^2\right)+\left(69^2-19^2\right)=\left(81-31\right)\left(81+31\right)+\left(69-19\right)\left(69+19\right)=50.112+50.88=50\left(112+88\right)=50.200=10000\)

Answer 3

=(812−312)+(692−192) = (81−31)(81+31)+(69−19)(69+19)=50.112+50.88=50(112+88)=50.200=10000