# Challenge Math Challenge - April 2019

#### Master1022

@Master1022 as I check again High School problem $1 c$ I see that you mean that the total sum is $1$ plus a new layer (=possible positions) each time and the series is on even numbers, so you finally mean $(n + 1)^2$ but the way is written is more cumbersome than it needs to. So, what is the difference from $n$ being odd?
I realised after posting that they were the same, but not when I was working through the mathematics.

#### Master1022

Let's take it in a simple way. We are moving along a diagonal - whichever it is. If we meet our target (=destination) we're done. If not , there is a simple way to state what you do according to where is the destination relatively to the point on the diagonal that you are. That's all I ask. The way you describe it is as taking another diagonal etc. Is this the optimal way?
Thank you for your response. I fail to see how my method doesn't get a king/piece to the destination square in an optimal number of moves. In response to your suggestion, I will keep thinking. At first, I thought about closest approach (i.e. you move diagonally until the direction between you and the destination is perpendicular to the diagonal you move on, but that only works if destination square is of the same colour as the diagonal). Would you be able to explain what is redundant in my method which is basically "move diagonally towards the destination until you are below/above/left/right it, then move straight towards it"?

#### QuantumQuest

Gold Member
I realised after posting that they were the same, but not when I was working through the mathematics.
So, in both cases it is $(n + 1)^2$ squares and you get the credit for it.

As a simpler way to analyze and state the whole thing, you can say that starting from a certain square whether white or black, for each new $n$, we take into account all the squares of the same color ($n$ even) or the opposite color ($n$ odd) that are on the "border" - created by these squares, plus the squares of the same color (with the ones on the border) inside it.

#### QuantumQuest

Gold Member
Would you be able to explain what is redundant in my method which is basically "move diagonally towards the destination until you are below/above/left/right it, then move straight towards it"?
The way you state the steps in post #66 - taking also into account the diagram in your post #72, is basically correct but you can state it in a simpler manner - as you do in the above quote i.e. Move diagonally towards the destination until the king reaches the row or column that includes the destination and then move in a straight line. Describing it this way, it is obvious that if king is already on the same row or column with the destination then there will be zero diagonal moves.

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