Math Help

Archive for May, 2009

Question: Math Help with linear functions help please?

Find equation of the line. Through (5,-6); perpendicular to y=9. ok i know the answer is x=5 but i can’t figure out how they got it. i find the slope M=0+6 over 0-5 which gives me a slope of -6/5. then i do y+6=5/6(x-5) 5/6 because it’s the reciprocal of -6/5. then i get 6y+36=5x-25 then get 6y=5x-61 and this is as far as i get i know its wrong but i’m doing how the book says. its not really clear on this type of question so appreciate the help.

Answer: First of all, your use of the slope equation in m = (0+6)/(0-5) assumes that the line passes through (0,0), which isn’t true. So forget about the slope being -6/5 and all your subsequent calculations are wrong.

Now, back to the problem. You know the line is perpendicular to y=9. You should know that y=9 is a horizontal line with a slope of 0. The only line in the two dimensional plane that is perpendicular to a horizontal line is a vertical line, which has undefined slope. A vertical line, you should know, is in the form of x=?. Since this vertical line passes through (5,-6), x must be equal to 5. Thus, the line is x=5

Applications of Linear Functions – YourTeacher.com – Math Help