(√98 - √20) / (√5 + √7) =

=(√98 - √20) (√5 - √7)
__________× ______
(√5 + √7) (√5 - √7)

=√490 - √686 - √100 - √140
________________________
5 - √35 + √35 - 7

=√70.√7 + √98.√7 - 10 - √20.√7
________________________
-2

=(√70 + √98 -√20)√7 - 10
___________________
-2

=√188.√7 -10
__________
-2
=√188 . √7 + 5

gak nemu, tapi yang paling mendekati yang (C)