For all x, (3x + 7) ² = ?

A. 6x + 14

B. 6x² + 14

C. 9x² + 49

D. 9x² + 21x + 49

E. 9x² + 42x + 49

Can anyone explain how to make it step by step?

When u see square that means u have to multiply the number by it self.

(3x + 7) * (3x + 7)

3x * 3x = 9x^2

3x * 7 = 21x

7 * 3x = 21x

7 * 7 = 49

Now u have 9x^2 + 21x + 21x + 49

Now u have to combine like terms meaning u have to add the number that have the same variable (x)

21x + 21x = 42x

Answer: E.) 9x^2 + 42x + 49