Question 121334
Can you please help me understand the method of arriving at the answer of this problem? Thank you. 
In my textbook this was the exercise question
Write the product in standard form:
(2+3i)(2-i) 
<pre><font size = 4><b>

   F        O          I         L       
(2)(2) + (2)(-i) + (3i)(2) + (3i)(-i)

   4   -   2i    +    6i   -   3i²

             4 + 4i - 3(-1)
           
              4 + 4i + 3

                7 + 4i



The answer in the back of the book was 
X= -4 +or- the sqrt of the fraction 8/3. 

I don't understand how they arrived at this answer.

I don't either. I think you looked at the answer
to this problem instead:

Solve for x by completing the square:

       3x² + 24x + 40 = 0

            3x² + 24x = -40

              x² + 8x = {{{-40/3}}}

8·1/2 = 4, 4² = 16, so add + 16 to both sides

         x² + 8x + 16 = {{{-40/3}}} + 16

       (x + 4)(x + 4) = {{{-40/3}}} + {{{48/3}}}

             (x + 4)² = {{{8/3}}}

Use square root principle:
                         
                x + 4 = ±{{{sqrt(8/3)}}}

                    x = -4 ± {{{sqrt(8/3)}}}

Edwin</pre>