Question

Write an equation for the line that passes through (0,7) and is perpendicular to the line whose equation is y=1/2x-1.

y-y1=m(x-x1)
y-7=2/1(x-0)
y-7=2x-0
y=2x+7(answer)

Answer 1

The slope of the line you want is -2.
(y-7) = -2(x-0)
y = -2x + 7

Answer 2

Where did you get negative 2??

Answer 3

The product of the slopes of two perpendicular lines has to be -1. That should be in your textbook or class notes somewhere.

(1/2) * -2 = -1