Question

bài 1 :rút gọn

a, (3x-1)(9x²+3x+1)=27x³-1

b, (x²-5x+25)(x+5)=x³+125

c, (x-3)(x²-6x+9)=(x-3)³

d, (x-y+4)(x+y-4)

e, x³y⁵(2xy³-y⁷)-y⁷(-x³y⁵+2)

Answer 1

a) (3x-1)(9x²+3x+1)=27x³-1

27x³-1=27x³-1

27x³-1-(27x³-1)=0

27x³-1-27x³+1=0

⇒x=0

b)(x²-5x+25)(x+5)=x³+125

(x+5)(x²-x.5+5²)=x³+125

x³+125-(x³+125)=0

x³+125-x³-125=0

⇒x=0

c)(x-3)(x²-6x+9)=(x-3)³

x³-3³-(x-3)³=0

x³-27-x³+27=0

⇒x=0

Answer 2

d) Đề phải là thế này chứ \(\left(x-y+4\right).\left(x-y-4\right)\)

\(=\left(x-y\right)^2-4^2\)

\(=\left(x-y\right)^2-16\)

\(=x^2-2.x.y+y^2-16\)

\(=x^2-2xy+y^2-16.\)

Chúc bạn học tốt!