a) 27x6 = 3*9*6 = 162

b) 99x4 = 11x9x4 = 396

c) 125x16 = 5x5x5x4x4=2000

Lời giải:

$A=(99-97)+(95-93)+(91-89)+...+(7-5)+(8-1)$

$=\underbrace{2+2+2+...+2}_{24}+7$

$=2\times 24+7$

$=55$

Câu 1:

(x-18)-42=(23-43)-(70+x)

x-18-42=-20-70-x

x-18-42+20+70+x=0

2x+30=0

2x=-30

x=-15

Câu 2 : Tính tổng

a,1+(-2)+3+(-4)+...+19+(-20)

Từ 1 đến -20 có 20 số hạng 

=> Có 10 nhóm

=>(1-2)+(3-4)+...+(19-20)

=-1-1-1-....-1

=-1.10

=-10

b,c,d,e làm tương tự ta được : 

b) -50

c) -24

d) -99

e) -100

Câu 3 : Tìm x

a)\(x\left(x+7\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x+7=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=0\\x=-7\end{cases}}}\)

Vậy : x={0;-7}

b)\(\left(x+12\right)\left(x-3\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x+12=0\\x-3=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=-12\\x=3\end{cases}}}\)

Vậy:....

c)\(\left(-x+5\right)\left(3-x\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}-x+5=0\\3-x=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=5\\x=3\end{cases}}}\)

Vậy:......

d)\(x\left(2+x\right)\left(7-x\right)=0\)

\(\Leftrightarrow\hept{\begin{cases}x=0\\2+x=0\\7-x=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=0\\x=-2\\x=7\end{cases}}}\)

Vậy:.....

e) \(\left(x-1\right)\left(x+2\right)\left(-x-3\right)=0\)

\(\Leftrightarrow\hept{\begin{cases}x-1=0\\x+2=0\\-x-3=0\end{cases}\Leftrightarrow\hept{\begin{cases}x=1\\x=-2\\x=-3\end{cases}}}\)

Vậy:........

Câu 4 : 

a) ab+ac

=a(b+c)

b) ab-ac+ad

=a(b-c+d)

c) ax-bx-cx+dx

=x(a-b-c+d)

d) a(b+c)-d(b+c)

=(b+c)(a-d)

e) ac-ad+bc-bd

=a(c-d)+b(c-d)

=(c-d)(a+b)

f) ax+by+bx+ay

=x(a+b)+y(a+b)

=(a+b)(x+y)

#H

bạn giải chi tiết giúp mik ý d,e câu 2 đc k.Mik k hiểu chỗ đó

16.19

=16.(20-1)

=320-16

=304

46.99

=46.(100-1)

=4600-46

=4554

35.98

=35.(100-2)

=3500-70

=3430

16.(20-1)=320-16=304

46.(100-1)=4600-46=4554

35.(100-2)=3500-70=3430

   Đây là câu trả lời của mình:

16.19 = 16( 20 - 1)= 320- 16 =304

46.99= 46.( 100-1)= 4600- 46= 4554

35.98= 35.( 100- 2) = 3500-70= 3430

13.19=13.(20-1)=13.20-1=260-1=259

46.99=46.(100-1)=46.100-1=4600-1=4599

35.98=35.(100-2)=35.100-2=3500-2=3498

k mình nha

16.19 = 16 (20-1) = 16.20 - 16.1 = 320 - 16 = 304

46.99 = 49. (100 - 1) = 49.100- 49.1 = 4900 - 49 = 4851

35. 98 = 35. (100-2) = 35.100 - 35.2 = 3500 - 70 = 3430

16 . 19 = 16 . (20 - 1) = 16 . 20 - 16 = 320 - 16 = 304

46 . 99 = 46 . (100 - 1) = 46 . 100 - 46 = 4600 - 46 = 4554

35 . 98 = 35 . (100 - 2) = 35 . 100 - 35 . 2 = 3500 - 70 = 3430

B1:

\(a.301^2=\left(300+1\right)^2=300^2+2.300.1+1^2\\ =90000+600+1=90601\\ b.88^2+2.88.12+12^2=\left(88+12\right)^2=100^2=10000\\ c.99.100=100^2-100=10000-100=9900\\ d,153^2+94.153+47^2=153^2+2.153.47+47^2=\left(153+47\right)^2=200^2=40000\)

B2:

\(A=x^2-20x+101\\ =x^2-2.x.10+10^2+1\\ =\left(x-10\right)^2+1\ge1\forall x\in R\left(Vì:\left(x-10\right)^2\ge0\forall x\in R\right)\\ \Rightarrow min_A=1\Leftrightarrow x-10=0\Leftrightarrow x=10\)

16.(20-1)=320-16=304

46.99=46.(50-1)=2300-46=2554

35.(100-2)=3500-70=3430

16 . 19 = 16(20 - 1) = 320 - 16 = 304;

46 . 99 = 46(100 - 1) = 4600 - 46 = 4554;

35 . 98 = 35(100 - 2) = 3500 - 70 = 3430.

16 . 19 = 16(20 - 1) = 320 - 16 = 304;

46 . 99 = 46(100 - 1) = 4600 - 46 = 4554;

35 . 98 = 35(100 - 2) = 3500 - 70 = 3430.

`a)(1-1/2)xx(1-1/3)xx(1-1/4)xx(1-1/5)`

`=1/2xx2/3xx3/4xx4/5`

`=[1xx2xx3xx4]/[2xx3xx4xx5]`

`=1/5`

`b)(1-3/4)xx(1-3/7)xx(1-3/10)xx(1-3/13)xx .... xx(1-3/97)xx(1-3/100)`

`=1/4xx4/7xx7/10xx10/13xx .... xx94/97xx97/100`

`=[1xx4xx7xx10xx...xx94xx97]/[4xx7xx10xx13xx....xx97xx100]`

`=1/100`

a) \(\left(145\times99+145\right)-\left(143\times102-143\right)\)

\(=\left[145\times\left(99+1\right)\right]-\left[143\times\left(102-1\right)\right]\)

\(=\left(145\times100\right)-\left(143\times101\right)\)

\(=14500-14443\)

\(=57\)

b) \(54\times47-47\times53-20-27\)

\(=47\times\left(54-53\right)-20-27\)

\(=47-20-27\)

\(=0\)

c) \(10000-47\times72-47\times28\)

\(=10000-47\times\left(72+28\right)\)

\(=10000-47\times100\)

\(=10000-4700\)

\(=5300\)

d) \(3457-27\times48-48\times73+6543\)

\(=\left(3457+6543\right)-48\times\left(27+73\right)\)

\(=10000-48\times100\)

\(=10000-4800\)

\(=5200\)