Given: sine of cap A is equal to 4 fifths , pi over 2 is less than cap A comma cap A is less than pi and sine of cap b is equal to the fraction with numerator negative 2 square root of 5 and denominator 5 , pi is less than cap b comma cap b is less than 3 pi over 2 What is the value of cosine of open paren cap A minus cap b close paren ?