Пусть tgx=t.
Тогда, как известно, cos2x = (1-t²)/(1+t²)
cos2x = (1-0.04)/(1+0.04)
cos2x = 0.96/1.04
cos2x = 12/13
2x = 2πn₁+cos⁻¹(12/13) n₁ ∈ Z
x = πn₁+ 1/2 cos⁻¹(12/13) n₁ ∈ Z
