Question

the fact that $(3i)^2=-9$ means that $3i$ is a square root of $-9$. check your understanding what is $(4i)^2$?

Explanation:

Step1: Apply exponent - rule

$(4i)^2=4^2\times i^2$

Step2: Calculate square of 4

$4^2 = 16$

Step3: Recall value of $i^2$

$i^2=-1$

Step4: Multiply results

$16\times(-1)= - 16$

Answer:

$-16$