Chứng minh rằng nếu $A \setminus B=A$ thì $A\cap B=\emptyset$. Giải: Giả sử $A\cap B\neq \emptyset \Rightarrow \exists x \in A \cap B$. Suy ra $x \in B \, ^{(1)}$ và $x \in A \, ^{(2)}$. Từ $(1)$ suy ra $x \notin A \setminus B$. Mà $A \setminus B=A$ nên $x \notin A$ (mâu thuẫn với (2)).
Phương pháp chứng minh nào đã được sử dụng?
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d. Phản chứng

-3

step-by-step explanation:

a drawing really does here:

so i draw the horizontal line y=2 and the vertical line x=-2 at this intersection i put b (this is where my right angle is going to be).   so point b is at (-2,2).   point a is 5 units long and is also on y=2 so this point has to be (3,2) or (-7,2) -doesn't matter i will go with (3,2).

now we know c is at (-2,y) we don't know the y yet bet we know that c is on x=-2.

we have the area of the triangle is .5bh=12.5

we know the base length is 5 (ab)

we have the height is (2-y) if you look at your

plug in

.5(5)(2-y)=12.5

solve for y to get the y-coordinate for c

2.5(2-y)=12.5

divide both sides by 2.5 giving:

2-y=5

now subtract 2 on both sides

-y=3

y=-3

47.28 or 47.2857143

step-by-step explanation:

you just divide 331 by 7 and you get that answer. ( i think so tho)