Question

. help me guys please​

Answer 1

Answer:

Bacteriophages are virus that infect bacteria. Phage literally means eaters of bacteria. The T4 phage that infects the bacterium Escherichia coli consists of a polyhedral head attached to a helical tail, a shape commonly found in bacteriophages. Many phages have tail fibers that attach to the host cell.

Step-by-step explanation:

Answer 2

Step-by-step explanation:

5)

Given set is A = {x:x+3 = 3 and x € N }

A is an empty set .

Reason :-

Put x = 1 then x+3 = 1+3 = 4

Put x = 2 then x+3 = 2+3 = 5

If we put x = 1,2,3...

We get { 4,5,6...}

So there is no natural number for x to get x+3 = 3

So ,There is no element to write for the set A

A is an empty set .

Note :-If x€W then x+3 = 0+3 = 3 then A is not an empty set .

6)

i) Given that { 1,4,9,16,...,100}

It can be written as { 1²,2²,3²,4²,5²,...10²}

Set builder form :-

=> A = {x:x = n², n≤10,n€N}

ii) {a,e,i,o,u}

These are vowels in the English alphabet

Set builder form:-

=> B = {x:x is a vowel in English alphabet }

7)

Given sets are A = { 1,20,30}

B = { 4,6}

Now,

A-B = { 1,20,30} -{ 4,6}

=> A-B = { }

Since there are no common elements in both A and B sets

=>Number of elements in A-B = 0

=> n(A-B) = 0

Therefore, n(A-B) = 0

Points to know:-

Empty set :-

A set having no element is called an empty set or void set or null set .It is denoted by phi or { }

The cardinal number of the Null set = 0

Difference of two sets :-

A and B are two sets ,The set of elements which belongs to A and does not belong to B is called The difference between the two sets A and B and it is denoted by A-B.

Cardinal number of a set :-

The number of all distinct elements in a set is called its Cardinal number .

It is denoted by n(A).