Answer:
first identify the like terms;
(2-7i)+(3+9i)
(2+3-7i+9i)
5+2i
Yes it's A cos that's the correct answer
Answer:
6.25
Step-by-step explanation:
Answer:

--- Variance
Step-by-step explanation:
Given

Solving (a): Calculate the mean.
The given data is a grouped data. So, first we calculate the class midpoint (x)
For 51 - 58.

For 59 - 66

For 67 - 74

For 75 - 82

For 83 - 90

So, the table becomes:

The mean is then calculated as:



-- approximated
Solving (b): The sample variance:
This is calculated as:

So, we have:


-- approximated
The area of a triangle is one half the area for a rectangle because the triangle is half of a rectangle with equal base and height