Odd times even equals? Why

Odd times even equals? Why

Odd times even = even
For example
1*2=2
3*8=24
5*4=20
.
So odd times even = even. You don't have to say. Fill in the blanks, but the application questions need to be solved

Which two singular numbers add up to the singular and which three singular numbers add up to the even?
The whole problem is that there are 36 flowers in 7 vases. Each vase must be singular

The title must be wrong

Root (25-x2) - root (15 + x2) = 4 find root (25-x2) + root (15-x2)

Radical (25-x2) - radical (15-x2) = 4
Numerator Rationalization
((25-x2) - (15-x2)) / (radical (25-x2) + radical (15-x2)) = 4
Radical (25-x2) + radical (15-x2) = 5 / 2