Use the given conditions to write an equation for the line in point-slope form and general form.
passing through (1,−7) and perpendicular to the line whose equation is x−2y−5=0

Hello there is solution :   
an equation for the line in point-slope form and general form is :
y = ax+b   a : slope  ; the Passing through (x' ; y')
y' = ax'+b 
y-y' =a(x-x')      and : x' =1   y' =-7
calculate a :
let :  y = ax+b (D)
     x-2y-5 =0  (D')
.(D) perpendicular to(D') : slope (D) × slope (D') = -1 
but / x-2y-5 =0      2y = x-5
y = (-1/2)x-5/2
 slope (D') = -1/2
slop(D)×(-1/2) = -1
slope (D) = 2
equation for the line    :   y-y' =a(x-x') 
y+7 =2 (x-1)
y = 2x-9