Thầy, không phải anh

Bài 1

a) 2x(x + 3) + 2(x + 3)

= (x + 3)(2x + 2)

= 2(x + 3)(x + 1)

b) 4x(x - 2y) + 8y(2y - x)

= 4x(x - 2y) - 8y(x - 2y)

= (x - 2y)(4x - 8y)

= 4(x - 2y)(x - 2y)

= 4(x - 2y)²

c) y²(x² + y) - zx² - zy

= y²(x² + y) - (zx² + zy)

= y²(x² + y) - z(x² + y)

= (x² + y)(y² - z)

d) 3x(x + 7)² - 11x²(x + 7) + 9(x + 7)

= (x + 7)[3x(x + 7) - 11x² + 9]

= (x + 7)(3x² + 21x - 11x² + 9)

= (x + 7)(-8x² + 21x + 9)

= (x + 7)(-8x² + 24x - 3x + 9)

= (x + 7)[(-8x² + 24x) - (3x - 9)]

= (x + 7)[-8x(x - 3) - 3(x - 3)]

= (x + 7)(x - 3)(-8x - 3)

e) (x + 5)² - 3(x + 5)

= (x + 5)(x + 5 - 3)

= (x + 5)(x + 2)

f) 2x(x - 3) - (x - 3)²

= (x - 3)(2x - x + 3)

= (x - 3)(x + 3)

g) x(x - 7) + (7 - x)²

= x(x - 7) + (x - 7)²

= (x - 7)(x + x - 7)

= (x - 7)(2x - 7)

h) 3x(x - 9)² - (9 - x)²

= 3x(x - 9)² - (x - 9)²

= (x - 9)²(3x - 1)

i) 5x(x - 2) - (2 - x)

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

= (x - 2)(5x + 1)

j) 4x(x + 1) - 8x²(x + 1)

= (x + 1)(4x - 8x²)

= 4x(x + 1)(1 - 2x)

o) 5x⁵(x - 2z) + 5x⁵(2z - x)

= 5x⁵(x - 2z) - 5x⁵(x - 2z)

= 0

p) 10x(x - y) - 8y(y - x)

= 10x(x - y) + 8y(x - y)

= (x - y)(10x + 8y)

= 2(x - y)(5x + 4y)

r) 2x(x + 1) + 2(x + 1)

= (x + 1)(2x + 2)

= 2(x + 1)(x + 1)

= 2(x + 1)²

t) 4x(x - 2y) + 8y(2y - x)

= 4x(x - 2y) - 8y(x - 2y)

= (x - 2y)(4x - 8y)

= 4(x - 2y)(x - 2y)

= 4(x - 2y)²

d) 3x(x - 1) + 7x²(x - 1)

= (x - 1)(3x - 7x²)

= x(x - 1)(3 - 7x)

e) x²y²z + xy²z² + x²yz

= xyz(xy + yz + x)

f) 2x(x + 1) + 2(x + 1)

= (x + 1)(2x + 2)

= 2(x + 1)(x + 1)

= 2(x + 1)²

g) 4x(x - 2y) + 8y(2y - x)

= 4x(x - 2y) - 8y(x - 2y)

= (x - 2y)(4x - 8y)

= 4(x - 2y)(x - 2y)

= 4(x - 2y)²

a) 3a(x - y) + 2b(y - x)

= 3a(x - y) - 2b(x - y)

= (x - y)(3a - 2b) chia hết cho 3a - 2b

b) 5^(n + 1) - 5^n

= 5^n(5 - 1)

= 5^n.4 chia hết cho 4

c) x³ - x

= x(x² - 1)

= x(x - 1)(x + 1) chia hết cho x + 1

Lớp 5 xài dấu nhân này nhé em "×"

Chiều dài thửa ruộng:

55,5 × 5 : 3 = 92,5 (m)

Diện tích thửa ruộng:

92,5 × 55,5 = 5133,75 (m²)

Số ngô thu hoạch được từ thửa ruộng:

5133,75 : 100 × 30 = 1540,25 (kg) = 15,4025 (tạ)

cot a = 1/3

Suy ra tan a = 1 : 1/3 = 3

1/cos² a = 1 + tan² a = 1 + 9 = 10

Suy ra cos² a = 1/10

Suy ra cos a = căn(10)/10

sin²a + cos²a = 1

Suy ra sin²a = 1 - cos²a = 1 - 1/10 = 9/10

Suy ra sin a = 3 căn(10)/10

\(144⋮x;420⋮x\Rightarrow x\inƯC\left(144;420\right)\) và \(x>2\)

144 = 2⁴.3²

420 = 2².3.5.7

\(\RightarrowƯCLN\left(144;420\right)=2^2.3=12\)

\(\RightarrowƯC\left(144;420\right)=\left\{1;2;3;4;6;12\right\}\)

\(\Rightarrow x=3;x=4;x=6;x=12\)

Not friend, I'm a math's teacher

\(2x+10=3x-20\)

\(3x-2x=10+20\)

\(x=30\)

Chọn A