Since the foci (±3, 0) lie on x-axis.
∴ The equation of ellipse in standard form is

x2

a2

+

y2

b2

= 1
Now, foci are (±3, 0) ⇒ c = 3
We know that c2 = a2–b2
∴ (3)2 = (4)2–b2 ⇒ b2 = 16 – 9 = 7.
Hence the required equation of ellipse is

x2

16

+

y2

7

= 1.