Multiply 40 by 40 and find two numbers that add up to 100, and multiply to 1600.
40 and 40? No. That adds to 80.
20 and 80? Yes. That adds to 100.
so you do \(40n^2+80n+20n+40\)
Simplify and continue doing so.
\(=40n(n+2)+20(n+2)\)
Now this is when you put together the numbers so that distributive property works out in your favour.
\(=(40n+20)(n+2)\)
Simplify. \(=20(2n+1)(n+2)\) There you go.
