Question

1. Tính:

a) ( 3x+1) (3x-1) ; ( x+5y) (x-5y)

b) ( x-3) (x^2+3x+9) ; (x-5) (x^2+5x+25)

2. Rút gọn biểu thức:

a) (x+1) ^2 - (x-1)^2-3 (x+1) (x-1)

b) 5(x+2) (x-2) - (2x-3) ^2-x^2+17

c) (x-1) ^3-(x-1)(x^2+x+1)

d) (x-3) ^3-(x-3)(x^2+3x+9) +6(x+1) ^2

3. Tìm x:

a) (x+4) ^2-(x+1)(x-1) =16

b) (2x-1) ^2+(x+3) ^2-5(x+7) (x-7) = 0

c) (x-2) ^3-(x-4)(x^2+4x+16) +6(x+1) ^2=49

d) (x+2)(x^2-2x+4) -x(x^2+2) =15

Answer 1

1

a) \(\left(3x+1\right)\left(3x-1\right)=9x^2-1\)

\(\left(x+5y\right)\left(x-5y\right)=x^2-25y\)

b) \(\left(x-3\right)\left(x^2+3x+9\right)=x^3-27\)

\(\left(x-5\right)\left(x^2+5x+25\right)=x^3-125\)

Answer 2

Bài 3:

a: \(\Leftrightarrow x^2+8x+16-x^2+1=16\)

=>8x+1=0

=>x=-1/8

b: \(\Leftrightarrow4x^2-4x+1+x^2+6x+9-5x^2+245=0\)

=>2x+255=0

=>x=-255/2

c: \(\Leftrightarrow x^3-6x^2+12x-8-x^3+64+6x^2+12x+6=49\)

=>24x+62=49

=>24x=-13

=>x=-13/24

d: =>x^3+8-x^3-2x=15

=>-2x=15-8=7

=>x=-7/2