MEDAL AND FAN FOR WHOEVER HELPS ME!!!!
Lily is practicing multiplying complex numbers using the complex number (2 + i).
To determine the value of (2+i)^2 , Lily performs the following operations:

Question

MEDAL AND FAN FOR WHOEVER HELPS ME!!!!
Lily is practicing multiplying complex numbers using the complex number (2 + i).
To determine the value of (2+i)^2 , Lily performs the following operations:

anonymous · Answer

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anonymous · Answer

Lily made an error.  Explain Lily's error and correct the step which contains the error.

r.hamza17 · Answer

Here, just re-read the question once again. The mistake made is is opening the square. As (a+b)^2= a^2+b^2+2ab so the mistake made by lilly is that she had not used the formula for opening the square.
Now use, 
(2+i)^2= 2^2+i^2+4i

anonymous · Answer

i have a question. where do you get the 4i from?

r.hamza17 · Answer

As in the formula a^2+b^2+2ab, so in the question when expanding (2+i)^2, we get 2*2*i=4i

anonymous · Answer

oh okay i get it. But now how would i change step 2 or is it okay?