√- 81 doesn't result in a rational number because you can't get a negative from squaring any number. Instead you get a number with an imaginary number.
13 - √- 81 = 13 - 9i
Answer:

Step-by-step explanation:
Given
Shape: Cylinder



Required
Simplify the volume
The volume is calculated as:

Substitute values for Base Area and Height

Expand the bracket

Open brackets



Answer:
a = -4/9
Step-by-step explanation:
(9a + 4) = 0
Subtract 4 from each side
9a + 4-4 = 0-4
9a = -4
Divide each side by 9
9a/9 = -4/9
a = -4/9
8+11=19. So there’s 19 roses in total