=-5145

k mk nha bn

-39 . ( 5 - 99 ) + 99 . ( 10 - 99 )

= ( -39 ) . ( -94 ) + 99 . ( -89 )

= 3666 + ( -8811 ) 

= -5145

\(-39\cdot\left(5-99\right)+99\cdot\left(10-99\right)\)

\(=-39\cdot5-\left(-39\right)\cdot99+99\cdot10-99\cdot99\)

\(=-39\cdot5+39\cdot99+99\cdot10-99\cdot99\)

\(=-39\cdot5+99\cdot\left(39+10-99\right)\)

\(=-39\cdot5+99\cdot50\)

\(=-195+4950\)

\(=4755\)

-39 x ( 5 - 99 ) + 99 x ( 10 - 39 )

= -39 x 5 - 39 x ( -99 ) + 99 x 10 - 99 x 39

=  -39 x 5 + [ 39 x 99 - 99 x 39 ] + 99 x 10

= -39 x 5 + 99 x 10

= -39 x 5 + 198 x 5

= 5 x ( -39 + 198 )

= 5 x 159

= 795

-39.(5-99)+99.(10-39)

=-39.(-94)+99.(-29)

=3666+(-2871)

=795

Ta có: 99x99=99x(98+1) = 99x98+99

98x100= 98x(99+1) = 98x99+98

Ta có: 98x99=98x99 mà 99> 98 => 99x99>98x100

giai ro rang

 (-1)+2-3+4-....-99+100 = 50

1 + 1³ + 1⁴ + ............. + 1⁹⁸ + 1⁹⁹ (98 số hạng)

= 1 + 1 + 1 + 1 + .......... + 1 (98 số hạng)

= 98 . 1

= 98

      \(\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{1}{2}-\frac{1}{3}+-\frac{1}{6}\right)\)

\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)

\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{3}{6}-\frac{2}{6}-\frac{1}{6}\right)\)

\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times0\)

\(=0\)

\(\frac{1}{99.97}-\frac{1}{97.95}-...-\frac{1}{3.1}\)

\(\frac{1}{99}-\frac{1}{97}-\frac{1}{97}-\frac{1}{95}-...-\frac{1}{3}-1\)

\(\frac{1}{99}-1\)

\(-\frac{98}{99}\)

\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)