The true statement about the directrix is that each directrix of this ellipse is 31.25 units from the center on the major axis.
<h3>How to determine the distance of the directrix?</h3>
The equation of the ellipse is given as:

The above means that:
a^2 = 625
a = 25
b^2 = 225
b = 15
Calculate c using:
c^2 = a^2 - b^2
This gives
c^2 = 625 - 225
Evaluate the difference
c^2 = 400
Evaluate the square root
c = 20
The equation of the directrix is
x - x₀ = ± a²/c
So, we have:
x - x₀ = ± 625/20
Evaluate the quotient
x - x₀ = ± 31.25
This means that, each directrix is 31.25 units from the center on the major axis.
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Answer:
the element must be in the fifth, sixth, or seventh energy shells.
Explanation:
Because the first ionization energy is less than calcium's, the element must be larger and in the next energy shell. Calcium is in the fourth energy shell, so the element must be in the fifth, sixth, or seventh energy shells.
Answer:
22
Explanation:
Plug 3 into x and solve. 3 x 5 is 15 plus 7 is 22