Lol
What you have to do is move the top point(s) down a grid at a time, keeping them symmetrical until the endpoint and sliderend nearly line up. Then disable grid snap and move the top point down until it's exact. Ctrl + H to check.
Also I find that it's easiest to make your points symmetrical if you do it roughly at first, then Ctrl+H and see what moves. Then you can fix based on that. You can also use the switch to grid two method if you prefer.
What you have to do is move the top point(s) down a grid at a time, keeping them symmetrical until the endpoint and sliderend nearly line up. Then disable grid snap and move the top point down until it's exact. Ctrl + H to check.
Also I find that it's easiest to make your points symmetrical if you do it roughly at first, then Ctrl+H and see what moves. Then you can fix based on that. You can also use the switch to grid two method if you prefer.