Can someone please explain the answers?

Answer:
3. Fifth degree polynomials are also known as quintic polynomials. Quintics have these characteristics: One to five roots. Zero to four extrema.
4. x = -5 or x = 0 or x = 5
Step-by-step explanation:
Solve for x:
6 x^5 - 150 x^3 = 0
The left hand side factors into a product with four terms:
6 x^3 (x - 5) (x + 5) = 0
Divide both sides by 6:
x^3 (x - 5) (x + 5) = 0
Split into three equations:
x - 5 = 0 or x^3 = 0 or x + 5 = 0
Add 5 to both sides:
x = 5 or x^3 = 0 or x + 5 = 0
Taking cube roots gives 0 times the third roots of unity:
x = 5 or x = 0 or x = 0 or x = 0 or x + 5 = 0
Subtract 5 from both sides:
x = 5 or x = 0 or x = 0 or x = 0 or x = -5
There are {2} duplicate solutions:
Answer: x = -5 or x = 0 or x = 5