我可以找到余弦逆来找到三角形的角度吗

Question

I am trying to find the angle of a triangle I have complete most of the work using this formula

now Problem is that how to find cos inverse in PHP I have the code below to find the cosine inverse

echo acos(42/90);

it returns a float value, not angle.

Answer 1

Trigonometric functions work with radians, not degrees, so you have to calculate

$AngleInDegrees = rad2deg(acos(42/90))
or
$AngleInDegrees = acos(42/90) * 180 / Pi();