Question

Answer 1

a)Ta có \(\dfrac{\left(a+b\right)^2-\left(a-b\right)^2}{4}=ab\)

⇒\(\left(a+b-a+b\right)\left(a+b+a-b\right)=4.ab\)

\(\Rightarrow2b.2a=4ab=vếphải\)(đpcm)

 

Answer 2

c) x²+y²=(x+y)²\(-2xy\)

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

\(\Rightarrow\left(x+y\right)^2=VP\left(đpcm\right)\)

 

Answer 3

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

\(\Rightarrow\left(a+b\right)^2-\left(a-b\right)\left(a+b\right)-2b\left(a+b\right)=0\)

\(\Rightarrow\left(a+b\right)\left(a+b-a+b-2b\right)=0\)

\(\Rightarrow\left(a+b\right).0=0=VP\left(đpcm\right)\)

Answer 4

d: Ta có: \(\left(a+b\right)^2-\left(a-b\right)\left(a+b\right)\)

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

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

c:Ta có: \(x^2+y^2\)

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

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