# showing that a complex number is a square root to another complex number

i have this question in calculus which i don't understand fully. My teacher is not replying and i have around 3 hours to solve this, so i'm gonna ask here and hope for someone to help me.

the exercises says: let $d = -3+4i.$

show that the number $u = 1+2i$ is the square root for d, $(u^2=d)$

i do not really understand what the problem is, could someone please explain? no need to give me the answer right away, but to explain the problem here.

• Just compute $u^2$ and compare with $d$. – Wuestenfux Sep 15 '18 at 12:24
• i can't be more stupid... thanks for the answer – Hanna Sep 15 '18 at 12:46
• It is more correct to say that $u$ is a square root of $d$. There is another one, $-1-2i$ – Ross Millikan Sep 15 '18 at 22:43