newC wrote:

In the xy plane line m has the equation 4x + y = k. Line n passes through the origin and is perpendicular to line m. If point p has the coordinates (r, r+1) and is on both line n and m what is the value of r?

A. -4/3

B. 1/4

C. -4

D. 3/4

E. 4/3

Can anybody help me with this problem?! I really have no idea how to attack this problem..

Thanks!!

You can approach by calculating slopes of both lines m and n.

As we know both m and n lines are perpendicular;

slope m* slope n= -1slope of m= -4 since 4x=y+k =>(Y=

mx+c), where

m is slope

now calculate slope of n. as we know line passes through origin (0,0) and (r, r+1)

slope = (y2-y1)/(x2-x1) => (r+1-0)/(r-0) => (r+1)/r

lines are perpendicular; thus we can multiply both slopes

(r+1)/r*-4=-1 gives r= -4/3

Hence Ans is A.

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