# Day 4 – Working with these weird radian things There are often times that we’re forced to supply angles in radians rather than degrees, here’s one you might recognise:

```// startAngle and endAngle must be given in radians! ctx.arc(x, y, radius, startAngle, endAngle, anticlockwise);```

Luckily we can convert between degrees and radians, because one degree is equal to PI / 180 radians:

```var one_degree_in_radians = 1 * Math.PI / 180; var five_degrees_in_radians = 5 * Math.PI / 180;```

Conversely, one radian is equal to 180 / PI degrees:

```var one_radian_in_degrees = 1 * 180 / Math.PI; var five_radians_in_degrees = 5 * 180 / Math.PI;```

So let’s use this knowledge to create variables that make converting between degrees and radians easier:

```// One degree in radians var TO_RADIANS = Math.PI / 180;   // One radian in degrees var TO_DEGREES = 180 / Math.PI;   var three_degrees_in_radians = 3 * TO_RADIANS; var two_radians_in_degrees = 2 * TO_DEGREES;```

Nothing can stop us now…

```// 360 degree arc ctx.arc(10, 10, 50, 0, 360 * TO_RADIANS, false);   // Sine, Cosine, etc require angles in radians: var sineX = Math.sin(90 * TO_RADIANS);``` 