# 4.1 Linear functions  (Page 11/27)

 Page 11 / 27

A vertical line    indicates a constant input, or x -value. We can see that the input value for every point on the line is 2, but the output value varies. Because this input value is mapped to more than one output value, a vertical line does not represent a function. Notice that between any two points, the change in the input values is zero. In the slope formula, the denominator will be zero, so the slope of a vertical line is undefined.

A vertical line, such as the one in [link] , has an x -intercept, but no y- intercept unless it’s the line $\text{\hspace{0.17em}}x=0.\text{\hspace{0.17em}}$ This graph represents the line $\text{\hspace{0.17em}}x=2.$

## Horizontal and vertical lines

Lines can be horizontal or vertical.

A horizontal line    is a line defined by an equation in the form $\text{\hspace{0.17em}}f\left(x\right)=b.$

A vertical line    is a line defined by an equation in the form $\text{\hspace{0.17em}}x=a.$

## Writing the equation of a horizontal line

Write the equation of the line graphed in [link] .

For any x -value, the y -value is $\text{\hspace{0.17em}}-4,\text{\hspace{0.17em}}$ so the equation is $\text{\hspace{0.17em}}y=-4.$

## Writing the equation of a vertical line

Write the equation of the line graphed in [link] .

The constant x -value is $\text{\hspace{0.17em}}7,$ so the equation is $\text{\hspace{0.17em}}x=7.$

## Determining whether lines are parallel or perpendicular

The two lines in [link] are parallel lines    : they will never intersect. They have exactly the same steepness, which means their slopes are identical. The only difference between the two lines is the y -intercept. If we shifted one line vertically toward the other, they would become coincident.

We can determine from their equations whether two lines are parallel by comparing their slopes. If the slopes are the same and the y -intercepts are different, the lines are parallel. If the slopes are different, the lines are not parallel.

Unlike parallel lines, perpendicular lines    do intersect. Their intersection forms a right, or 90-degree, angle. The two lines in [link] are perpendicular.

Perpendicular lines do not have the same slope. The slopes of perpendicular lines are different from one another in a specific way. The slope of one line is the negative reciprocal of the slope of the other line. The product of a number and its reciprocal is $\text{\hspace{0.17em}}1.\text{\hspace{0.17em}}$ So, if are negative reciprocals of one another, they can be multiplied together to yield $\text{\hspace{0.17em}}–1.$

${m}_{1}{m}_{2}=-1$

To find the reciprocal of a number, divide 1 by the number. So the reciprocal of 8 is $\text{\hspace{0.17em}}\frac{1}{8},\text{\hspace{0.17em}}$ and the reciprocal of $\text{\hspace{0.17em}}\frac{1}{8}\text{\hspace{0.17em}}$ is 8. To find the negative reciprocal, first find the reciprocal and then change the sign.

As with parallel lines, we can determine whether two lines are perpendicular by comparing their slopes, assuming that the lines are neither horizontal nor vertical. The slope of each line below is the negative reciprocal of the other so the lines are perpendicular.

The product of the slopes is –1.

#### Questions & Answers

sinx sin2x is linearly dependent
what is a reciprocal
The reciprocal of a number is 1 divided by a number. eg the reciprocal of 10 is 1/10 which is 0.1
Shemmy
Reciprocal is a pair of numbers that, when multiplied together, equal to 1. Example; the reciprocal of 3 is ⅓, because 3 multiplied by ⅓ is equal to 1
Jeza
each term in a sequence below is five times the previous term what is the eighth term in the sequence
I don't understand how radicals works pls
How look for the general solution of a trig function
stock therom F=(x2+y2) i-2xy J jaha x=a y=o y=b
sinx sin2x is linearly dependent
cr
root under 3-root under 2 by 5 y square
The sum of the first n terms of a certain series is 2^n-1, Show that , this series is Geometric and Find the formula of the n^th
cosA\1+sinA=secA-tanA
Wrong question
why two x + seven is equal to nineteen.
The numbers cannot be combined with the x
Othman
2x + 7 =19
humberto
2x +7=19. 2x=19 - 7 2x=12 x=6
Yvonne
because x is 6
SAIDI
what is the best practice that will address the issue on this topic? anyone who can help me. i'm working on my action research.
simplify each radical by removing as many factors as possible (a) √75
how is infinity bidder from undefined?
what is the value of x in 4x-2+3
give the complete question
Shanky
4x=3-2 4x=1 x=1+4 x=5 5x
Olaiya
hi can you give another equation I'd like to solve it
Daniel
what is the value of x in 4x-2+3
Olaiya
if 4x-2+3 = 0 then 4x = 2-3 4x = -1 x = -(1÷4) is the answer.
Jacob
4x-2+3 4x=-3+2 4×=-1 4×/4=-1/4
LUTHO
then x=-1/4
LUTHO
4x-2+3 4x=-3+2 4x=-1 4x÷4=-1÷4 x=-1÷4
LUTHO
A research student is working with a culture of bacteria that doubles in size every twenty minutes. The initial population count was  1350  bacteria. Rounding to five significant digits, write an exponential equation representing this situation. To the nearest whole number, what is the population size after  3  hours?
f(x)= 1350. 2^(t/20); where t is in hours.
Merkeb