Cost a=0.6489

take the inverse cosine of both sides

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
: It looks like this in the calculator
 × cos A=(0.6489)
( and cos cancels out)
A=(0.6489)
A=49.54°
check: 
cos 49.54=0.6489 (its right!)

1+1=22×1=22-1=11-1=1duh