38.
sec^6(x)(sec(x)tan(x))-sec^4(x)(sec(x)tan(x))=sec^5(x)tan^3(x)
sec^6(x)(sec(x)tan(x))-sec^4(x)(sec(x)tan(x))
=sec^6(x)(sec(x)tan(x))-sec^4(x)(sec(x)tan(x))........tan(x)=sec(x)/csc(x)
=sec^6(x)(sec(x)(sec(x)/csc(x)))-sec^4(x)(sec(x)(sec(x)/csc(x)))
=sec^5(x)((sec^3(x)/csc(x)))-sec^5(x)((sec(x)/csc(x)))
=sec^5(x)((sec^3(x)/csc(x))-(sec(x)/csc(x)))
=sec^5(x)((sec^2(x)(sec(x)/csc(x))-(sec(x)/csc(x)))
=sec^5(x)((sec^2(x)tan(x)-tan(x)))
=sec^5(x)((sec^2(x)-1)tan(x))
=sec^5(x)tan^2(x)tan(x)
=sec^5(x)tan^3(x)
42. correct