Answer
$(10d+1)^2$
Work Step by Step
The first term is $10d$ squared, the last term is $1$ squared, and the middle term is twice the product of these two terms. Now we can factor the trinomial into a binomial squared.
$100d^2+20d+1$
$=(10d+1)(10d+1)$
$=(10d+1)^2$
