Question

26. Which of the following is an equation for the line that is perpendicular to the line y = 2x - 9

and passes through the point (-4,5)?

A. y = 2x+7
B. y = -1/2x+3
C. y = 2x+5
D. y = -14x-9

Answer 1

y = -1/2x + 3

Explanation:

We know that if two lines are perpendicular to each other the multiplication of the slopes of those 2 lines equals -1.

m₁ × m₂ = -1

Given that, the slope of one line is 2 (m₁). Now, let us find the slope of the other line (m₂) using the above formula.

2 × m₂ = -1

2m₂ = -1

Divide both sides by 2.

m₂ = -1/2

And now let us find the value of the y-intercept ( c in the formula y = mx + c) using the given coordinate.

( -4 , 5 )⇒ ( x , y ).

Let us find it now.

y = mx + c

5 = -1/2x × -4 + c

5 = 2 + c

5 - 2 = c

3 = c

And now let us write the equation for the new line.

y = m x + c

y = -1/2x + 3

Answer 2

y = -1/2x+3

Explanation:

We have y = 2x-9

This is in slope intercept form

y = mx+b where m is the slope

The slope is 2

We want a line that is perpendicular

Perpendicular lines have slopes that are negative reciprocals

The slope is -1/2

The equation of the new line is

y = -1/2x+b

Substituting the point into the equation

5 = -1/2(-4)+b

5 = 2+b

5 -2=b

3=b

y = -1/2x+3