or
use Lhopitals rule to get the derivatives of the numerator and the denominator.
Your numerator is incomplete...
If x is 49, the numerator is 49(7)+49(7)-49(7)-7(49)
which means we've gotten nowhere!
Both numerator and denominator are still zero if x=49.
This is because we are still subtracting equal quantities in both numerator and denominator.
Notice how Harish's method leaves us without subtractions.