Since the foci (±5, 0) lie on x-axis.
∴ The equation of ellipse in standard form is

x2

a2

+

y2

b2

= 1
Now, length of major axis 2a = 26 ⇒ a = 13, Foci are (±5, 0) ⇒ c = 5
Also, we know that c2 = a2–b2 ⇒ 52 = (13)2–b2 ⇒ b2 = 169 – 25 = 144.
Hence the required equation of ellipse is

x2

169

+

y2

144

= 1