The correct option is option 3: (a + b)2 = a2 + 2ab + b2.
In this equation, (a + b)2 represents the square of the sum of a and b. The term a2 represents the square of the value of a, b2 represents the square of the value of b, and 2ab represents the product of twice the value of a and b.
The equation (a + b)2 = a2 + 2ab + b2 is an expansion of the binomial formula (a + b)2, which states that the square of a binomial expression is equal to the sum of the squares of the individual terms and twice the product of the terms.
Therefore, option 3 correctly indicates the equation (a + b)2 = a2 + 2ab + b2.