Hint: Use the tools to create a point along a line or curve.
Plus use the Bezier Curve Tool with control handles for important curves, this enables precise control for copying/scaling/manipulating/etc.
Also, it helps to know the constraints for the pattern
Example: For jeans/pants, the front inseam curve from crotch to knee is a bit shorter than the back inseam curve from crotch to knee, and the extra fullness is sewn in as ease so the pants fit properly around the thigh. The tighter the fit at the knee, the larger the difference between the front & back inseam curves. Similarly, there is ease in the outseam from hip line to knee, which is greater when the knee is close-fitting (or the hips are large), and non-existent for stove-pipe trousers. This ease is important for good fit, and is usually 'built-in' to the formulas for jeans, pants, trousers. (if your jeans are made from stretchy denim then you won't have this ease.)
But there are three sections of the pants inseams & outseams where the lengths must match between front & back.
1. From knee to hem inseam
2. From knee to hem outseam
3. From waist to hip outseam
To check these lengths:
1. To create the back inseam from knee to hem: Use Point from length and angle tool at the knee. Use the length and angle from the front inseam's knee to hem line.
2. To create the back outseam from knee to hem: Use Point from length and angle tool at the knee. Use the length and angle from the front outseam's knee to hem line.
3. Create the back hip curve as directed by your pattern formulas. Pick the outseam hip point, and create a point along the curve (going up toward the waist) using the length of the front outseam waist to hip curve. Create the back waist line using the new point on the back hip curve.