\(xy+3x-7y=23\)

\(\Leftrightarrow x\left(y+3\right)-7y-21=2\)

\(\Leftrightarrow x\left(y+3\right)-7\left(y+3\right)=2\)

\(\Leftrightarrow\left(x-7\right)\left(y+3\right)=2=1.2=2.1=\left(-1\right).\left(-2\right)=\left(-2\right).\left(-1\right)\)

Lập bảng:

Vậy \(\left(x,y\right)\in\left\{\left(8,-1\right);\left(9,-2\right);\left(6,-5\right);\left(5,-4\right)\right\}\)

Ảnh nhìn dê vãi (tởm)

\(C=\left(1-\frac{1}{1931}\right)\left(1-\frac{1}{1932}\right)\left(1-\frac{1}{1933}\right).....\left(1-\frac{1}{2019}\right)\)

\(C=\frac{1930}{1931}\cdot\frac{1931}{1932}\cdot\frac{1932}{1933}\cdot\cdot\cdot\cdot\cdot\frac{2018}{2019}\)

\(C=\frac{1930\cdot1931\cdot1932\cdot\cdot\cdot\cdot\cdot2018}{1931\cdot1932\cdot1933\cdot\cdot\cdot\cdot\cdot2019}=\frac{1930}{2019}\)

(1-1/1931).(1-1/1932).(1-1/1933).........(1-1/2019)

= (1930/1931).(1931/1932).(1932/1933)......(2018/(2019)

= 1930/2019

       @ Hc tốt nha cj !!!!

trả lời 

Câu hỏi của Nguyễn Ngọc Thảo My - Toán lớp 5 - Học toán với OnlineMath

vào thống kê !!! 

aa) -(345+96345+96)+(−155+1996−155+1996)

=−345−96−155+1996=−345−96−155+1996

== (−345−155−345−155) - (96−199696−1996)

=−500+1900=−500+1900

=1400=1400

bb) (−456+95−456+95)-(-456+95456+95)-192192

=−456+95+456−95−192=−456+95+456−95−192

== (−456+456−456+456) + (95−9595−95) -192192

=−192=−192

cc) (a−b+ca−b+c)- (c−bc−b)+aa

=a−b+c−c+b+a=a−b+c−c+b+a

== (a+aa+a) + (−b+b−b+b) + (c−cc−c)

=2a=2a

dd)-(a−b+ca−b+c)+(c−bc−b)+aa

=−a+b−c+c−b+a=−a+b−c+c−b+a

== (−a+a−a+a) + (b−bb−b) + (−c+c−c+c)

=0=0

ee) (a−b+ca−b+c)+(c−bc−b)+aa

=a−b+c+c−b+a=a−b+c+c−b+a

== (a+aa+a) + (−b−b−b−b) + (c+cc+c)

=2a−2b+2c

sao có những chỗ liên tiếp vậy bn?

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

 = a + b + c - b + c - d

 = a + 2c - d

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

 = a + b - c + a - b + d

 = 2a - c + d

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

 = a + b + a - b + c

 = 2a + c

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

 = -a - b + a + b + c

 = c

Học tốt~

\(9.9+9\)

\(=\left(9.9\right)+9\)

\(=81+9\)

\(=90\)

a = 0; b = 3; c = 5

k nhé

a) a.a.a.b.b = a³.b²

b)m.m.m.m+p.p = m⁴+p²