I was thinking the same thing, but I wasn't sure what to call the scratch variable.

Or, maybe something like this:
```javascript
this._ti = Cartesian3.multiplyByScalar(
	Cartesian3.subtract(
		Cartesian3.subtract(
			Cartesian3.multiplyByScalar(controlPoint1, 2.0),
			controlPoint2
		),
		controlPoint0
	), 0.5);
```