Question

What is the equation of the line perpendicular to y=1/2x+6 that passes through the point (4, 1)?

Answer 1

Answer:

A

Step-by-step explanation:

Find the slope of the perpendicular line.

The slopes are related by the formula

m1 * m2 = - 1

Since m1 is 1/2, m2 must be -2

So far what you have is y = -2x + b

Find the y intercept (b).

The new line goes through (4,1)

x = 4

y = 1

1 = -2(4) + b

1 = - 8 + b  

b = 1 + 8

b = 9

The answer is

y = - 2x + 9

Answer 2

Answer:

A. y = -2x + 9

Step-by-step explanation:

The slope-intercept form of an equation of a line:

$y=mx+b$

m - slope

b - y-intercept

Let  $k:y=m_1x+b_1,\ l:y=m_2x+b_2$

then

$l\ \perp\ k\iff m_1m_2=-1\to m_2=-\dfrac{1}{m_1}\\\\l\ \parallel\ k\iff m_1=m_2$

We have the equation of the line:

$y=\dfrac{1}{2}x+6\to m_1=\dfrac{1}{2}$

therefore a slope of a line perpendicular to given line has the slope:

$m=-\dfrac{1}{\frac{1}{2}}=-2$

Put the value of slope m = -2 and the coordinates of the point (4, 1) to the equation of a line:

$1=-2(4)+b$

$1=-8+b$           add 8 to both sides

$9=b\to b=9$

Finally:

$y=-2x+9$