This seems like a very simple problem, but I am getting confused.
When you multiply out say $(x+4)^2$ then it is the same as $x(x + 4) + 4(x + 4)$, so I believe the correct output would be $x^2 + 8x + 16$
However, on a video I am following there is the equation $3(x-1)^2 - 5$, where $x = 3$.
In the video they simply work out by doing:
= $3(3-1)^2 - 5$
= $3(2)^2 - 5$
= $3(4) - 5$
= $7$
I am confused why this equation doesn't follow the same formula as used in the $(x + 4)^2$ example. i.e. why doesn't it work to do $3(x(x - 1) - 1(x - 1)) - 5$ which would be:
= $3(x(x - 1) - 1(x - 1)) - 5$
= $3(x^2 -2x + 2) - 5$
= $3x^2 - 6x + 6 - 5$
= $3(3)^2 - 6(3) + 1$
= $27 - 18 + 1$
= $10$
I realize this is probably very very basic, but it is still confusing to me, so I would be very thankful for any help.