Question

find the value of cos 105°

Answer 1

cos 60=
$\sqrt{32}$
cos 45=
$\sqrt{22}$

cor 105 =
$\sqrt{32 } + \sqrt{22}$

Answer 2

Step-by-step explanation:

Cos (105°) = Cos (60° + 45°)

∴Cos ( A + B) = CosA . CosB - SinA . SinB

Use the formula and Solve

Cos (105°) = Cos(60° + 45°)

                = Cos60° . Cos45° - Sin60° . Sin45°

                = 1/2 . 1/√2 - √3/2 . 1/√2

                = 1/2√2 - √3/2√2

                = 1 - √3/ 2√2