Two discrete mathematical problems, seeking the solution of great spirit 1. Prove with reasoning rules: if the premise "all zebras have stripes" and "mark is a zebra" are true, then the conclusion "mark has stripes" is true 2. Prove that "if the earth is flat, then you can drive to the edge of the earth"; "you can't drive to the edge of the earth". Therefore, "the earth is not flat" is an effective argument

Two discrete mathematical problems, seeking the solution of great spirit 1. Prove with reasoning rules: if the premise "all zebras have stripes" and "mark is a zebra" are true, then the conclusion "mark has stripes" is true 2. Prove that "if the earth is flat, then you can drive to the edge of the earth"; "you can't drive to the edge of the earth". Therefore, "the earth is not flat" is an effective argument

1. Firstly, the proposition is symbolized, and the individual field is the total individual field
P (x): X is a zebra; Q (x): X has stripes; a: mark
Premise: ax (P (x) → Q (x)); P (a);
Conclusion: Q (a)
Certification:
(1) the introduction of ax (P (x) → Q (x))
(2) P (a) → Q (a) ① UI rules
(3) the introduction of P (a) premise
(4) Q (a) (2) hypothetical reasoning
So it is proved
　　
2. First, the proposition is symbolized and recorded
P: the earth is flat; Q: you can drive to the edge of the earth;
Premise: P → Q, q
Conclusion: p;
Certification:
(1) the introduction of P → Q premise
(2) P ∨ Q (1) permutation
The introduction of Q premise
Disjunctive syllogism
It has been proved
Note: the above statements are all from Qu Wanling's discrete mathematics

The following formula () is neither true nor false. A.P ←→ Q B.P ←→┓ P C.P → P d.c.p →┓ p

A: choose C

An undirected tree T has six leaves and four three degree branch points. The other branch points are all four degree vertices. How many vertices does t have?
How to calculate dizziness

e=v-1
E is the number of edges, V is the number of nodes, assuming that the number of vertices of degree 4 is X
Tree (graph) also has a theorem: the sum of degrees of all nodes is twice the number of edges
Six leaves, degree 1
So: 6 + 12 + 4x = 2v-2 = 2 * (6 + 4 + x) - 2
Find out that x is 0
So the title is wrong

Why is the row rank of any matrix equal to the column rank of a matrix?
Of course, I will prove that the row rank of a matrix is equal to the column rank of a matrix. What I want to ask is why it looks like this?

I know what you mean. You want to say why the simplest form of ladder matrix looks like row rank is more than column rank or vice versa. In fact, when you transpose the matrix and simplify it, you will find that the row rank or column rank that looks more in the original ladder matrix will always be reduced to the same rank as the matrix. If you don't believe it, you can try