Answer: -4
Explanation:
If homogenous equation ax^2+2hxy+by^2=0---------------(a)
represent two perpendicular lines then, a+b=0
Calculation :
Given 3x² - 8xy + my² = 0
on comparing with equation (a) we get, a=3 and b=k
given lines are mutually perpendicular then
m+3= 0
m=-3