Through the hyperbola x ^ 2 / 4-y ^ 2 / 3 = 1, the left branch of the straight line intersection of the left focus F1 is at the Mn point, and F2 is its right focus, then the value of | MF2 | + | NF2 | - | Mn | is? I don't know where Mn = MF1 + NF1 comes from

Through the hyperbola x ^ 2 / 4-y ^ 2 / 3 = 1, the left branch of the straight line intersection of the left focus F1 is at the Mn point, and F2 is its right focus, then the value of | MF2 | + | NF2 | - | Mn | is? I don't know where Mn = MF1 + NF1 comes from

Mn is a line segment
F1 on line segment
So Mn = MF1 + NF1
Just draw a picture

A cuboid is 12 decimeters long, one third of its length in width and one fourth of its length in height
(volume)

Width: 12 × 1 / 3 = 4 decimeters
Height: 12 × 1 / 4 = 3 decimeters
The volume is: 12 × 4 × 3 = 144 cubic decimeter

1、3、3、5、7、9、13、15、（ ）
What number should be in brackets?

1、3、3、5、7、9、13、15、（21）
One by one, 1, 3, 7, 13, with a difference of 2, 4, 6
3,5,9,15, the difference is 2,4,6
The next difference is 8,13 + 8 = 21

Find the rules and fill in the blanks, 0,1,3,8,21, (), ()
Find the rules and fill in the blanks, 0,1,3,8,21, (), ()

1*1=1
1*3=3
2*4=8
3*7=21 (3=1+2 7+3+4)
5*11=55 (5+2+3 11=7+4)
8*18=144 (8=5+3 18=11+7)
Do you find a rule? The top two terms add up to the next