Question 551116
Plans for a bridge are drawn on a coordinate grid. One girder of the bridge lies on the line y = –9x – 9. A perpendicular brace passes through the point (–1, 7). Write an equation of the line that contains the brace.
A. y – 1 = –1/9(x + 7)
B. x – 7 = –9(y + 1)
C. y – 7 = 1/9( x + 1)
D. y – 7 = –9(x + 1) 


The equation we seek, must have a slope that is perpendicular to the slope of the given equation.  The product of perpendicular slopes = -1.


You were given y = -9x - 9.  The slope for this equation is -9.  What number times -9 will yield -1?  How about 1/9?


We know that the equation we need to find must have a slope of 1/9.


We use the slope 1/9 and the given point (-1,7) and plus this information into the point-slope formula.


y - y1 = m(x - x1)


y - 7 = (1/9)(x + 1)


The answer is choice C.