thuc hien phep tinh:-39.(5-99)+99.(10-99)
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-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
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Ta có: 99x99=99x(98+1) = 99x98+99
98x100= 98x(99+1) = 98x99+98
Ta có: 98x99=98x99 mà 99> 98 => 99x99>98x100
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1 + 13 + 14 + ............. + 198 + 199 (98 số hạng)
= 1 + 1 + 1 + 1 + .......... + 1 (98 số hạng)
= 98 . 1
= 98
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\(\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{1}{2}-\frac{1}{3}+-\frac{1}{6}\right)\)
\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{1}{2}-\frac{1}{3}-\frac{1}{6}\right)\)
\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times\left(\frac{3}{6}-\frac{2}{6}-\frac{1}{6}\right)\)
\(=\left(\frac{10}{99}+\frac{11}{199}-\frac{12}{299}\right)\times0\)
\(=0\)
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\(\frac{1}{99.97}-\frac{1}{97.95}-...-\frac{1}{3.1}\)
\(\frac{1}{99}-\frac{1}{97}-\frac{1}{97}-\frac{1}{95}-...-\frac{1}{3}-1\)
\(\frac{1}{99}-1\)
\(-\frac{98}{99}\)
=-5145
k mk nha bn
-39 . ( 5 - 99 ) + 99 . ( 10 - 99 )
= ( -39 ) . ( -94 ) + 99 . ( -89 )
= 3666 + ( -8811 )
= -5145