(145x99+145)-(143x101-143)

=145x(99+1)-143x(101-1)

=145x100-143x100

=14500-14300

=200

vì mọi số nhân vs 1 bằng chính nó mà

( 145 x 99 + 145 ) - ( 143 x 101 - 143 )

= ( 145 x ( 99 + 1 ) - ( 143 x ( 101 - 1 )

= 145 x 100 - 143 x 100

= 14500 - 14300

= 200

\(\frac79\times\frac{13}{17}\times\frac{17}{13}=\frac79\times\left(\frac{13}{17}\times\frac{17}{13}\right)\)

\(=\frac79\times1=\frac79\)

cảm ơn nhé

83,9*101

=83,9*100+83,9*1

=8390+83,9

=8473,9

1,2 : 1,8 x 0,3=0,2

1,2 : 1,8 x 0,3 = ( 1,2 x 0,3 ) : 1,8

                     = 0,4 : 1,8

                     =  0,2

Tính bằng cách thuận tiện nhất :

\(3,6\cdot4\cdot0,125\cdot2,5\cdot8\)

\(=3,6\cdot\left(4\cdot2,5\right)\cdot\left(0,125\cdot8\right)\)

\(=3,6\cdot10\cdot1\)

\(=36\)

570+150+430+850

=(570+430)+(150+850)

=1000+1000

=1000x2

=2000

570+150+430+850

=[570+430]+[150+850]

= 1000 + 1000

=  2000

\(=\frac{74+69}{75+89}\)\(=\frac{10}{13}\)

\(=\frac{2007.2009+2007-1007}{2007.2009+2009-1009}\)

\(=\frac{2007.2009+1000}{2007.2009+1000}\)

=1

(2004-1)(2004+1)+200/2004.2004+199

=2004^2-1+200/2004^2+199

=2004^2+199/2004^2+199

=1

\(\frac{2003.2005+200}{2004.2004+199}\)

= \(\frac{2003.\left(2004+1\right)+200}{\left(2003+1\right).2004+199}\)

= \(\frac{2003.2004+2003+200}{2003.2004+2004+199}\)

= \(\frac{2003.2004+2203}{2003.2004+2203}\)

= \(1\)

                 ~~~~Hok tốt~~~~