Bài 3 : 

\(D=40^2-28^2+32^2+80.32=40^2+2.40.32+32^2-28^2\)

\(=\left(40+32\right)^2-28^2=72^2-28^2=\left(72+28\right)\left(72-28\right)=46.100=4600\)

4600 nha

Bài 4 : 

\(B=\left(9+1\right)\left(9^2+1\right)...\left(9^{32}+1\right)\)

\(8B=\left(9^2-1\right)\left(9^2+1\right)...\left(9^{32}+1\right)=9^{64}-1\)

\(\Rightarrow B=\frac{9^{64}-1}{8}< 9^{64}-1\Rightarrow B< C\)

bài 5mn giúp em đc k ạ

a, \(A=x\left(3x+1\right)+3x+1=\left(x+1\right)\left(3x+1\right)\)

Thay x = 33 ta được : \(32.100=3200\)

b, \(B=xy+2x+2y+4=x\left(y+2\right)+2\left(y+2\right)=\left(x+2\right)\left(y+2\right)\)

Thay x = 98 ; y = 98 ta được : \(100.100=10000\)

10000 nha

help me ctv

help me

BC=80 

SA23

5x² - x³ - 12x 

= x ( 5x - x² - 12 )

= -x ( x² - 5x + 12 )

= -x [ ( x - 5/2 )² + 23/4 ]

d, D = 40² - 28² + 32² +80.32

    D = (40² + 2.40.32 + 32²) - 28²

    D = (40 + 32)² - 28²

    D = (40 + 32 - 28)(40 + 32 + 28)

    D = 44.100

   D = 4400

  e, E = 10.80,5 + 10.19,5 - 8.20,5 - 8. 79,5

      E =  10.(80,5 + 19,5) - 8.( 20,5 + 79,5)

      E = 10.100 - 8.100

     E = 100.(10-8)

     E = 200

F = 50² - 18² + 32² + 100.32

F = (50² - 18²) + 32.( 32 + 100)

F = (50 -18)(50+18) + 32. 132

F = 32.68 + 32.132

F = 32.( 68 + 132)

F = 32. 200

F = 6400

3213

+

3452

= 6665

6665 nha

g, sửa đề 

 \(5x^2-5xy+7y-7x=5x\left(x-y\right)+7\left(y-x\right)=\left(5x-7\right)\left(x-y\right)\)

h, sửa đề

 \(xy-xz+z-y=x\left(y-z\right)-\left(y-z\right)=\left(x-1\right)\left(y-z\right)\)

i, \(x^3+2x^2-3x-6=x^2\left(x+2\right)-3\left(x+2\right)=\left(x^2-3\right)\left(x+2\right)\)