a) (12,84+5,92) x 13,8= 18,76 x 13,8 = 258,888

b) (98,17 - 43,56)x 5,6 = 63,61 x 5,6 = 356,216

Bài 1:

\(a,=\left(156-56\right)^2=100^2=10000\\ b,=\left(x-y\right)^2-4z^2=\left(x-y-2z\right)\left(x-y+2z\right)\)

Bài 2:

\(a,=\left(x-y\right)\left(x+y\right)-5\left(x-y\right)=\left(x-y\right)\left(x+y-5\right)\\ b,=x^2+2x-6x-12=\left(x+2\right)\left(x-6\right)\\ c,=3\left(x^2-2xy-16+y^2\right)=3\left[\left(x-y\right)^2-16\right]\\ =3\left(x-y-4\right)\left(x-y+4\right)\)

a.54,01    

a.54,01

\(5,6=5,60=5,600=5,6000\)
\(34,56=34,560=34,5600=34,56000\)
\(35,08=35,080=35,0800=35,08000\)
\(8,900=8,90=8,9=8,9000\)

5,6=5,600

A= 12,45x7,8+12,45x92,2

= 12,45x(7,8+92,2)

=12,45x100

=1245

B=25,89x75,2-25,89x65,2

=25,89x(75,2-65,2)

=25,89x10

=258,9

C=34,56x23,9-34,56x12,4+11,5x65,44

=34,56x(23,9-12,4)+11,5x65,44

=34,56x11,5+11,6x65,44

=11,5x(34,56+65,44)

=11,5x100

=1150

\(A=12,45.7,8+12,45.92,2\)

\(A=12,45.\left(7,8+92,2\right)\)

\(A=12,45.100\)

\(A=1245\)

\(B=25,98.75,2-25,89.65,2\)

\(B=25,89.\left(75,2-65,2\right)\)

\(B=25,89.10\)

\(B=258,9\)

\(C=34,56.23,9-34,56.12,4+11,5.65,44\)

\(C=34,56.\left(23,9-12,4\right)+11,5.65,44\)

\(C=34,56.11,5+11,5.65,44\)

\(C=11,5.\left(34,56+65,44\right)\)

\(C=11,5.100\)

\(C=1150\)

 ( 5,6 x 27 + 56 x 3,5 ) : 6,2

=56(2,7+3,5):6,2

=56.6,2:6,2

=56

ko ghi lại đề bài 

=56.(2,7+3,5):6,2

=56:6,2:6,2

=56

hc tốt

ko ghi lại đề

=56.(2,7+3,5):6,2

=5,6.6,2:6,2

=5,6

hc tốt