# Math Help - Roots

1. ## Roots

Show that 4+i and -4-i are the sqaure rooots of 15 +8i

2. Originally Posted by meli3000
Show that 4+i and -4-i are the sqaure rooots of 15 +8i

It is sufficient to show that

$(4+i)^2=15+8i$

and that:

$(-4-i)^2=15+8i$

to show that $4+i$ and $-4-i$ are square roots of $15+8i$. (In fact it is sufficent to show that one of these is a square root since the other is minus one times it, and so also of necessity a square root of $15+8i$)

RonL

3. Originally Posted by meli3000
Show that 4+i and -4-i are the sqaure rooots of 15 +8i
Do you know how to square a binomial?
$(a+bi)^2=?$