Which of these numbers is the largest? 5 4 , 1.3, 10 9 , 6 4 , 1.6 a) 1.3 b) 1.6 c) 10 9 d) 4 4

C. 10 9 is the largest.

First we have to calculate the slope of line CD

C(1,1) D(3,5)
m = (y2 - y1)/(x2 - x1) 
m = (5-1)/(3-1) = 2

We know that two lines are perpendicular if this happens 
m1*m2 = -1

so
2*m2 = -1
m2 = -1/2 = -0.5

and finally the equation for a line is: y - y0 = m( x - x0)
y = -0.5x - 5.5