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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)
Write an equation in point-slope form of the line through point J(4, 1) with slope –49(x + 1)
Answer by nyc_function(2741)   (Show Source):
You can put this solution on YOUR website! 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.
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