Slopes of an Isosceles Triangle
Geometry · 26th PMO Qualifying Stage
Three lines with slope 1, 7, and $c$ intersect to form a nondegenerate isosceles triangle. If $1<c<7$, what is $c$?
A$\dfrac{8}{7}$
B$\dfrac{13}{7}$
C$2$
D$\dfrac{15}{7}$