For all x, (3x + 7)² = ?

A6x + 14
B6x² + 14
C9x² + 49
D9x² + 21x + 49
E9x² + 42x + 49

Can anyone explain how to make it step by step?

Verified Answer :

meme4

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