Question

Cost A=0.6489 take the inverse cosine of both sides

Answer 1

I am not quite sure what the question asks for,
But this is what i assume it wants:

Cos A= 0.6489
In this given one, we basically find the size of the angle A
we do cosine inverse on both sides to get the size of the angle A
$cos^{-1}$ : It looks like this in the calculator
$cos^{-1}$ × cos A=$cos^{-1}$(0.6489)
($cos^{-1}$ and cos cancels out)
A=$cos^{-1}$(0.6489)
A=49.54°
check: 
cos 49.54=0.6489 (its right!)