Question

CMR : 
a) ( a + b )^2 = a^2 + 2ab + b^2
b) ( a - b )^2 = a^2 - 2ab - b^2
c) a^2 - b^2 = ( a - b ).( a + b )
chú ý : a^2 là a mũ 2; ( a + b ) ^2
là ( a + b ) mũ 2 nha !
Mn giúp mik với : (

Answer 1

a, \(\left(a+b\right)^2=\left(a+b\right)\left(a+b\right)=a^2+ab+ab+b^2=a^2+2ab+b^2\)

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

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

 

Answer 2

\(a,\left(a+b\right)^2\\ =\left(a+b\right)\left(a+b\right)\\ =a^2+ab+b^2+ab\\ =a^2+2ab+b^2.\)

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

\(c,a^2-b^2\\ =a^2+ab-ab-b^2\\ =a\left(a+b\right)-b\left(a+b\right)\\ =\left(a-b\right)\left(a+b\right).\)