Answer :
2log7 - 2r = 0
1.690196080 - 2r = 0
-1.690196080 -1.690196080
-2r = -1.690196080
-2 -2
r = 0.84509804
1.690196080 - 2r = 0
-1.690196080 -1.690196080
-2r = -1.690196080
-2 -2
r = 0.84509804