Since sin(a) = , 


    cos(a) =  =  =  =  = .


Notice that since the angle "a" is in QI, cos(a) is positive; so, the sign of the square root is positive.


Next, since you know sin(a) and cos(a), you may calculate all other trigonometric functions  tan(a), cot(a), sec(a) and csc(a)


based on their definitions.

As  is ACUTE, the 6 TRIG. functions are in Quadrant 1.



As one of the legs is 3, and the hypotenuse is 5, it's then obvious that this is a PYTHAGOREAN triple, and so, the other leg (longer) will be 4.  

As such, we can see that 

The other 5 TRIG. functions are: 

Now, make the SUBSTITUTIONS. 

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