Hey there!!
In order to solve this problem, we will need to use the identity a² - b²
∴ a² - b² = ( a + b ) ( a - b )
According to the question,
a = a + b
b = b + c
( a + b )² - ( b + c )²
... ( a + b + b + c ) ( a + b - b - c )
... ( a + 2b + c ) ( a - c )
Now, we will need to solve this using distributive property.
Distribute a with a , 2b , c and distribute -c with a , 2b and c and then combine all the like terms.
... ( a² + 2ab + ac ) + ( -ac - 2bc - c² )
... ( a² + 2ab + ac - ac - 2bc - c² )
... ( a² + 2ab - bc - c² )
Hope my answer helps!!
