Question

Khai triển tích :

a) (a+1).(a-1)

b) (x+2).(x-2)

c) (x+y).(x+y)

d)(x+y).(x-y)

e)(x+3).(x-5)

f) (ab-2)(a^2.b^2+2ab+4)

Answer 1

nhanh nhé mk k cho

Answer 2

a) \(\left(a+1\right).\left(a-1\right)=a^2-a+a-1=a^2-1\)

b)\(\left(x-2\right).\left(x+2\right)=x^2-2x+2x-4=x^2-4\)

c)\(\left(x+y\right).\left(x+y\right)=x^2+xy+xy+y^2=x^2+2xy+y^2\)

d)\(\left(x+y\right).\left(x-y\right)=x^2-xy+xy-y^2=x^2-y^2\)

e) \(\left(x+3\right)\left(x-5\right)=x^2-5x+3x-15=x^2-2x-15\)

f)\(\left(ab-2\right).\left(a^2.b^2+2ab+4\right)=ab.\left(a^2.b^2+2ab+4\right)-2.\left(a^2.b^2+2ab+4\right)\)

\(=a^3.b^3+2a^2b^2+4ab-2.a^2.b^2-4ab-8\)

\(=a^3b^3-8\)

Lớp 8 thì các phương trình này đc khai triển ra bằng hằng đẳng thức

Answer 3

(a+1)(a-1)=a²-1

(x+2)(x-2)=x²-2²=x²-4

(x+y)(x+y)=(x+y)²=x²+2xy+y²

(x+y)(x-y)=x²-y²

(x+3)(x-5)=x²-5x+3x-15=x²-2x-15

(ab-2)(a²b²+2ab+4)=(ab-2)[(ab)²+2ab+2²]=(ab)³-2³=(ab)³-8