Solution Clarification

[notjames24]

I encountered this problem and its solution but I don't get why or how there is an 8 in the solution, would someone explain this?
Solution:

 

[Deleted member 4993]

I encountered this problem and its solution but I don't get why or how there is an 8 in the solution, would someone explain this?View attachment 27848
Solution:
View attachment 27849

Use the formula:

(x + y)² = x² + y² + 2 * x * y

In your case:

x = a

y = 4/a

2 * x * y = ?

 

[notjames24]

Ohhh, I see thank you so much!

 

[Steven G]

Why not get your hands dirty by multiplying out (a+4/a)^2 and what you get. Then you'll see where the 8 comes from.