\(25.5.4.125.20.8\)

\(=\left(25.4\right).\left(5.20\right).\left(125.8\right)\)

\(=100.100.1000\)

\(=10000000\)

25*(5+5)*4*20*8

=250*20+4+8

= 5000*12

=60000

đúng mk tích cho .

a)(147-25)-(-25+147-49)

=122-73

=49

b)57.(-28)+72.(-57)

=57.(-28-72)

=57.(-100)

=-5700

a.(147-25)-(-25+147-4)

= 147 - 25 + 25 - 147 + 4

= (147 - 147) + ( 25 - 25) + 4

= 0 + 0 + 4

= 4

b.57.(-28)+72.(-57)

= 57 . (-28) + (-72) . 57

= 57.((-28) + (-72))

= 57 . -100

= - 5700

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\(16=2^4\)

\(25=5^2\)

\(30=2\cdot3\cdot5\)

=>\(BCNN\left(16;25;30\right)=2^4\cdot5^2\cdot3=16\cdot25\cdot3=16\cdot75=1200\)

\(3,\\ 65=5.13\\ 80=5.2^4\\ BCNN\left(65;80\right)=5.13.2^4=1040\\ 4,\\ 16=2^4\\ 25=5^2\\ 30=2.3.5\\ BCNN\left(16;25;30\right)=2^4.3.5^2=1200\)

\(\frac{25}{1.6}+\frac{25}{6.11}+........+\frac{25}{86.91}\)

\(=5.\left(\frac{5}{1.6}+\frac{5}{6.11}+.....+\frac{5}{86.91}\right)\)

\(=5.\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+......+\frac{1}{86}-\frac{1}{91}\right)\)

\(=5.\left(1-\frac{1}{91}\right)\)

\(=\frac{90}{91}\)

1-1/6+1/6-1/11+....+1/86-1/91

1-1/91

90/91

\(\frac{25}{1.6}+\frac{25}{6.11}+....+\frac{25}{86.91}\)

\(=\frac{25}{5}.\left(\frac{5}{1.6}+\frac{5}{6.11}+.....+\frac{5}{86.91}\right)\)

\(=\frac{25}{5}.\left(\frac{1}{1}-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+....+\frac{1}{86}-\frac{1}{91}\right)=5.\left(1-\frac{1}{91}\right)=5.\frac{90}{91}=\frac{450}{91}\)

\(25-x^2-4xy-4y^2=5^2-\left(x+2y\right)^2=\left(5-x-2y\right)\left(5+x+2y\right)\)

=25-(x^2+4xy+4y^2)

=5^2-(x+2y)^2

=(5-x-2y)(5+x+2y)