ElectricPavlov

- sqrt(5/9)   =  -  sqrt 5  /  sqrt 9   =  -  ( sqrt 5) /  3

Be aware of where and how you use brackets.....they change the value of the answer if misplaced !

sin ?  = 2/3

arcsin (2/3) = 41.81 degrees

A gradian is a a different unit of measure for angles....a full circle is 400 gradians  (360 degrees).    I assumed that is what you meant to ask and just misspelled (as so often happens on this website)  'gradian' 

IF you really meant GRADIENT of an angle, it is most likely the tangent of the angle  (slope). 

A gradian is 9/10 of a degree    sooo   if you have 100 gradians    100 (9/10) = 90 degrees

or to go to gradians from degrees multiply by 10/9     90 degrees x 10/9 = 100 gradians

Just use tha calculator for these simple problems:

cos(x) = 25/32

arccos(x)  = arccos(25/32)

x = acos(0.78125) = 38.624832873053  degrees

4-2(2x-7) = -6

4 - 4x +14 = -6

-4x +18 = -6

-4x = -24

x = 24/4   =  6

Are   'N'    and  'n'  different variables ?    And what are you asking?

=  (.36)(.00081) =.002916

4850.1697  pounds

If you press the  '2nd'  key the 'cos' key becomes 'acos'    which is  cosine inverse or cos^-1