Which of the following equations describes a line that is
perpendicular to 3x + 7y = 9?

7x + 3y = 7
3x - 7y = 7
7y = -3x + 7
7x - 3y = 7

Question

Which of the following equations describes a line that is
perpendicular to 3x + 7y = 9?

7x + 3y = 7 
  3x - 7y = 7 
  7y = -3x + 7 
  7x - 3y = 7

nowhereman · Answer

Just take the vectors for the direction of the lines and check whether they are perpendicular, i.e. their scalar product is zero.

amistre64 · Answer

flip x and y and negate one.....the last one looks good

jit4won · Answer

if ax+by+c=0 be the equation of a line then equation of the line which is perpendicular to the given line is given by    bx- ay +d= 0 
so 7x-3y =7 is the answer