A = (-7,-6)
B = (8,-9)
Find the slope of line AB
m = (y2-y1)/(x2-x1)
m = (-9-(-6))/(8-(-7))
m = (-9+6)/(8+7)
m = -3/15
m = -1/5
The slope of line AB is -1/5.
Flip the fraction and the sign to go from -1/5 to +5/1 = 5. The perpendicular slope is 5.
Let m = 5.
Use the coordinates of point C (2,12) along with the perpendicular slope to get
y - y1 = m(x - x1)
y - 12 = 5(x - 2)
y - 12 = 5x - 10
y = 5x - 10+12
y = 5x + 2
Lastly, convert this to standard form
y = 5x + 2
5x+2 = y
5x+2-y = 0
5x-y = -2
Choice A is the closest match, but the -56 should be -2 instead. It seems like your teacher made a typo somewhere.
√(144*x²) = (√144)*(√x²) = 12x
Answer is D.12x.
