You need to know the properties of each function.
Tan is opposite (y) over adjacent (x). Sin>0 means that sin is positive, therefore, it is located on either quadrant 1 or 2. Tan=4/3 so it is located in quadrant 1.
The side of the triangle must be Adjacent=3 opposite=4 and hypotenuse=5
Now, you are asked to find the half angle of Cos which is
By following the formula, cos=3/5 then:
Multiply everything (inside the square 
root) by 5
Then just simplify
The answer is Square root of 20 over 5
Tan is opposite (y) over adjacent (x). Sin>0 means that sin is positive, therefore, it is located on either quadrant 1 or 2. Tan=4/3 so it is located in quadrant 1.
The side of the triangle must be Adjacent=3 opposite=4 and hypotenuse=5
Now, you are asked to find the half angle of Cos which is
By following the formula, cos=3/5 then: