Question

1.CM đẳng thức sau :

a) \(\left(a-b\right)^3=-\left(b-a\right)^3\)

b) \(\left(-a-b\right)^2=\left(a+b\right)^2\)

cần gấp . mn giúp mk với nhé mai mk nộp rồi !!!

Answer 1

\(a\text{)}\:VP=-\left(b^3+3a^2b-3ab^2-a^3\right)=a^2-3a^2b+3ab^2-b^3=\left(a-b\right)^3=VT\left(đpcm\right)\)

Answer 2

\(b\text{)}\left(-a-b\right)^2=\left[\left(-1\right)\left(a+b\right)\right]^2=\left(-1\right)^2.\left(a+b\right)^2=\left(a+b\right)^2\left(đpcm\right)\)

Answer 3

Ta có \(\left(a-b\right)^3=\)a³-3a²b+3ab²-b³-(b-a)^{3 (1)}

=-(b³-3ab²+3a²b-a³)=a³-3a²b+3ab²-b³ (2)

từ (1) và (2)=> (a-b)³=-(b-a)³ (đpcm)

b) ta có VT= (-a-b)²=[-(a+b)]²=(a+b)²=VP

vậy (-a-b)²=(a+b)²(đpcm)