Question 199715
Find the equation of a line that is perpendicular to the graph of 3x - 4y = - 21, and goes through the point (-1, 0). Write the answer in slope-intercept and standard form.


3x - 4y = - 21


Gives 4y = 3x + 21 or y = 3x/4 + 21/4 giving a gradient of 3/4


The product of the gradients of perpendicular lines equals - 1, so the gradient of the perpendicular line is - 4/3


As it passes through (-1, 0) we have 0 = - 4(-1)/3 + c; 0 = 4/3 + c; c = - 4/3;


y = - 4x/3 - 4/3 or 4x + 3y = - 4