# What's wrong with my math?

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Be quick and choose whether the shown equation is right or wrong.
• I'm trying to make this blue box orbit the red box using Cos & Sin, however the distance between the boxes is increasing.

Why? Shouldn't it stay the same distance away?

capx

• You want the angle you put into cos, and sin to be the same, and a value between 0, and 360. Use a variable and implement a counter to add to that variable.

Also you want to use the object that you want to rotate around as the x, and y.

Sprite.X+Cos(yourvariable)*distance(self.x,self.y,sprite.x,sprite.y)

Sprite.Y+Sos(yourvariable)*distance(self.x,self.y,sprite.x,sprite.y)

Then set yourvariable using the variable + something *dt.

Note it will probably work if you go beyond 360, but you can always use %360 as a limiter.

• But aren't the angles for sin & cos the same in my capx?

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• You used angle(), but you need that to either increase, or decrease.

• The reason the distance was increasing is because on every single tick it moves in a straight line that is 90 degrees from the direction to the centre.. In a sense it's not truly curved, the angle is just corrected 60 times a second.

Imagine what happens on a single tick, and if that distance was 200 pixels instead.. i think that makes it easier to see why it's moving further away from centre.. i hope .. I can totally understand the confusion though.

edit: you should try something like this, it's more or less what newt was saying.

<img src="https://dl.dropbox.com/u/53374990/Forum/orbit.png" border="0" />

• 5 posts