Answer:
[tex]tan75 {}^{0} = 2 + \sqrt{3} [/tex]
[tex]tan \: 15 {}^{0} = 2 - \sqrt{3} [/tex]
=> cot 75⁰ + cot 15⁰
= cot(90⁰ - 15⁰) + cot(90⁰ - 75⁰)
= tan 15⁰ + tan 75⁰
=
[tex]2 + \sqrt{3} + 2 - \sqrt{3} = 4[/tex]
(proven)
