Find the value of B - A if the graph of Ax + By = 3 passes through the point (-7, 2) and is parallel to the graph of x + 3y = -5.
From x + 3y = -5, y = -x/3 - 5, so the slope of the line is -1/3. The slope of the new line is also -1/3, so y = -x/3 + B. Pugging in x = 2 and y = -7, we get -7 = -2/3 + B, so B = -19/3.
Then the line is y = -x/3 - 19/3. Then 3y = -x - 19, so 3y + x = -19. We want the right-hand side to be 3, so we mutiply both sides by -3/19: -9/19*y - 3/19*x = 3. Therefore, B - A = -19/3 - 3 = -28/3.
Putting the equations into slope-intercept form,
y=−AxB+3B
y=−x3−53
Both lines are parallel, so −x3=−AxB. Simplify to find that AB=13, meaning that the slope is −13.
y=−x3+3B
Plug in (-7, 2).
2=−−73+3B
6B=7B+9
B=−9
Because A and B are in ratio AB=13, B = -9 and A = -3. So B - A = -9 - (-3) = -6
x + 3y = -5 re arrange to y = mx+b from:
y = -1/3 x - 5/3 slope = -1/3 ( parallel slope is the same)
y = -1/3 x - b sub in the given point to calculate 'b'
2 = -1/3 (-7) + b shows b = - 1/3
y = -1/3 x - 1/3 multiply by 3 to get rid of fraction
3y = 3x - 3
3x -3y = 3 then B - A = -3 - 3 = - 6