Answer:
a. closed under addition and multiplication
b. not closed under addition but closed under multiplication.
c. not closed under addition and multiplication
d. closed under addition and multiplication
e. not closed under addition but closed under multiplication
Step-by-step explanation:
a.
Let A be a set of all integers divisible by 5.
Let
∈A such that 
Find 

So,
is divisible by 5.

So,
is divisible by 5.
Therefore, A is closed under addition and multiplication.
b.
Let A = { 2n +1 | n ∈ Z}
Let
∈A such that
where m, n ∈ Z.
Find 

So,
∉ A

So,
∈ A
Therefore, A is not closed under addition but A is closed under multiplication.
c.

Let
but
∉A
Also,
∉A
Therefore, A is not closed under addition and multiplication.
d.
Let A = { 17n: n∈Z}
Let
∈ A such that 
Find x + y and xy


So,
∈ A
Therefore, A is closed under addition and multiplication.
e.
Let A be the set of nonzero real numbers.
Let
∈ A such that 
Find x + y

So,
∈ A
Also, if x and y are two nonzero real numbers then xy is also a non-zero real number.
Therefore, A is not closed under addition but A is closed under multiplication.
-7x - 2y = 19
4x + y = -12
Set y equal to each other (opposite signs are fine and you could also set x equal instead of y)
-7x - 2y = 19
8x + 2y = -76
Add equations together
x = -52
Plug x value into an equation
4(-52) + y = -12
Solve for y
-208 + y = -12
y = 196
Hope this helps! ;)
Answer:
Step-by-step explanation:
this is confusing b/c they are asking about two trains traveling at differnt speeds, but.. if you put the speeds together and make one train... imaginary.. ofc... traveling at the speed of both trains combined... when will it be 50 miles from the station?
maybe you can solve that? I'll solve it below.. but.. if you can.. try it now, on your own
below is my answer... don't look until you have solved yours :P
80+70= 150kph
when will this have traveled 50Km?
you may be able to see that it will take 1/3 of an hour to travel 50 km
so 60 minutes times 1/3 = 20 minutes :)
Answer:(x+2)(x−2)
Step-by-step explanation:Since both terms are perfect squares, factor using the difference of squares formula
<span>three million seventy thousand nine hundred</span>