Answer:
See proof below
Step-by-step explanation:
Let
. If w=-z, then r=0 and r is real. Suppose that w≠-z, that is, r≠0.
Remember this useful identity: if x is a complex number then
where
is the conjugate of x.
Now, using the properties of the conjugate (the conjugate of the sum(product) of two numbers is the sum(product) of the conjugates):

=
Thus
. From this,
. A complex number is real if and only if it is equal to its conjugate, therefore r is real.
It should be 13 since 13+8 = 21. 21-7 = 13
Answer:
12
Step-by-step explanation:
x = k/y Multiply each side by y
k = xy Insert values
= 6 × 72
= 432
x = 432/y Let y = 36
= 432/36
x = 12
2/5 x
----- = ----
100 2000
x=8