Answer
$9x^{2}+6xy+y^{2}+6x+2y+1$
Work Step by Step
$[(3x+y)+1]^{2}$
The square of a binomial can be found using the formula
$(a+b)^{2} = a^{2}+2ab+b^{2}$
$[(3x+y)+1]^{2}=(3x+y)^{2}+2(3x+y)(1)+1^{2}$
$=(3x+y)^{2}+2(3x+y)+1$
$=(3x)^{2}+2(3x)(y)+y^{2}+6x+2y+1$
$= 9x^{2}+6xy+y^{2}+6x+2y+1$
