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You need to give us more information. 
 
Is there one player and a target, or two players and a target? 
 
There are an infinite number of circles that go through player1 and target. 
 
Do you always want the center of the circle to be the midpoint between player1 and target. 
 
What is going to be moving? &nbsp;Is player1 constrained to move along the arc? 

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1) there is a RADIUS fixed: so I don't think there is a infinite number of solutions ! 
2) 1 player and 1 target 
3) yes center of the circle = middle point as I draw 
4) yes player1 is moving: that's why I put 
player1.x+=dx; 
player1.y+=dy; 
 
 
regards 

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&gt;&gt; &nbsp; 4) yes player1 is moving: that's why I put 
&nbsp; &nbsp; &nbsp; &nbsp; player1.x+=dx; 
&nbsp; &nbsp; &nbsp; &nbsp; player1.y+=dy; 
 
Except that you actually put &nbsp; player2.y+=dy 
 
That's why I was confused. 
 
You have to know what the radius is. 
Can you just call it R? 
 
Are the player and the target always at the same height/y-coordinate? 
 
You need either trig or simultaneous equations to find the center of the circle (Xo, Yo) 
 
Once you have the center, the path of player1 &nbsp;can be described by: 
&nbsp; &nbsp; &nbsp; 
 
 

<pre><code class="code-1 nolinks" id="code-8170839">player1.x = Xo + R*[cos(w*t + to)]

 player1.y = Yo + R*[sin(w*t + to)]
</code></pre>
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A 2D function (a circle in this case) can have more than one representation... 
i.e. 
1) 
&nbsp;y=f(x) where for every x point there’s a function f() that give us y 
 
2) 
y=f(t) 
x=g(t) 
in this case there's an auxiliary variable t; giving different values to “t” we get all the possible pairs (x,y) 
 
1) is used mostly for functions where for every x there’s only one correspondent y 
2) is used mostly when the former restriction does not apply 
 
a circle is a function that is almost always represented by 2) 
 
the former expert gave you the general equation of a circle where &quot;to&quot; is a constant representing the initial value of &quot;t&quot; 
w is called the &quot;angular speed&quot; &nbsp;w=2*pi*f where f is the &quot;frequency&quot; 
t as you know now is an auxiliary variable 
 
the names come from the fact that those equation represent many times in physics rotary movements 
then it results clear why w represents a speed and t really represents &quot;time&quot; 
 
then if you want to draw a circle on a screen 
you perform a loop in your code suplying t values to the eq then you get the (x,y) pairs and display them on the screen... 
 
 
 
 
 

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Given points (p1.x,p1.y),(p2.x,p2.y) and radius R, 
let D=sqrt((p1.x-p2.x)^2 + (p1.y-p2.y)^2) 
the centre of the circle would be at 
(c.x,c.y)=((p1.x+p2.x)/2 + (p1.y-p2.y)*z,(p1.y+p2.y)/2 + (p2.x-p1.x)*z) 
where z=sqrt(R^2-(D/2)^2))*2/D 
If the centre is at the midpoint of p1 and p2, then R=D/2 
 
then for an infinitesimal movement counter clockwize around the circle from p 
dx = (c.y-p.y)*dt 
dy = (p.x-c.x)*dt 
This becomes a perfect approximation as &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dt approaches 0, 
but for &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dt too large, p &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;will tend to spiral out &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;from c 

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<div class="content wysiwyg-content">
Hello experts 
&nbsp;I have to calculate dx and dy so player1 has a circular movement. 
(look at the embed picture: &nbsp; <a href="https://filedb.experts-exchange.com/incoming/2011/05_w21/460028/math.jpg" target="_blank" title="circular movement (13 KB)"><img alt="circular movement" class="file-block lazyload" style="max-width: 655px;" data-src="https://filedb.experts-exchange.com/incoming/2011/05_w21/460028/math.jpg" /></a> ) 
 
Thanks
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math.jpg

Hello experts
 I have to calculate dx and dy so player1 has a circular movement.
(look at the embed picture:    )

Thanks

circular movement: simple math algorithm

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Algorithms

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