Prime Set Operations
1. **State the problem:** We are given sets:
- $U = \{\text{all prime numbers}\}$
- $p = \{x : 8(x + 1) \geq 2 (x + 10)\}$
- $D = \{x : 7 < x < 31\}$
where $x$ is a prime number. We need to find:
a) $(p \cup D)'$
b) $p'$
c) $(p \cap D)'$
2. **Find set $p$:**
Solve inequality:
$$8(x + 1) \geq 2 (x + 10)$$
$$8x + 8 \geq 2x + 20$$
$$8x - 2x \geq 20 - 8$$
$$6x \geq 12$$
$$x \geq 2$$
Since $x$ is prime, $p = \{x : x \geq 2, x \text{ prime}\} = \{2,3,5,7,11,13,17,19,23,29,31, ...\}$
3. **Find set $D$:**
Given $7 < x < 31$ and $x$ prime, primes between 7 and 31 are:
$$D = \{11,13,17,19,23,29\}$$
4. **Find $p \cup D$: union of $p$ and $D$:**
Since $p$ includes all primes $\geq 2$, and $D \subset p$,
$$p \cup D = p$$
5. **Find complement of $p \cup D$ with respect to $U$: $(p \cup D)'$:**
Since $p \cup D = p$ and $U$ is all primes,
$$(p \cup D)' = p' = U \setminus p = \{ \text{prime numbers not in } p \}$$
But $p$ includes all primes $\geq 2$, and the smallest prime is 2, so no prime is excluded.
Hence,
$$(p \cup D)' = \emptyset$$
6. **Find $p'$ complement:**
As above,
$$p' = \emptyset$$
7. **Find $p \cap D$: intersection:**
Since $D \subset p$,
$$p \cap D = D = \{11,13,17,19,23,29\}$$
8. **Find $(p \cap D)'$: complement wrt $U$:**
$$(p \cap D)' = U \setminus D = \{\text{primes not in } D\} = \{2,3,5,7,31,37,41, ...\}$$
**Final answers:**
a) $(p \cup D)' = \emptyset$
b) $p' = \emptyset$
c) $(p \cap D)' = \{2,3,5,7,31,37,41, ...\}$ (all primes except those in $D$)