How to find the equation of a curve - Intermediate Geometry

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Question

If a line's -intercept is . and the -intercept is , what is the equation of the line?

Answer

Write the equation in slope-intercept form:

We were given the -intercept, , which means :

Given the -intercept is , the point existing on the line is . Substitute this point into the slope-intercept equation and then solve for to find the slope:

Add to each side of the equation:

Divide each side of the equation by :

Substituting the value of back into the slope-intercept equation, we get:

By subtracting on both sides, we can rearrange the equation to put it into standard form:

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Question

Find the -intercept of:

Answer

To find the x-intercept, we need to find the value of when .

So we first set to zero.

turns into

Lets subtract from both sides to move to one side of the equation.

After doing the arithmetic, we have

.

Divide by from both sides

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Question

What is the -intercept of:

Answer

To find the y-intercept, we set

So

turns into

.

After doing the arithmetic we get

.

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Question

What is the -intercept of:

Answer

The x-intercept can be found where

So

turns into

.

Lets subtract from both sides to solve for .

After doing the arithmetic we have

.

Divide both sides by

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Question

Suppose two intercepts create a line. If the -intercept is and -intercept is , what is the equation of the line?

Answer

Rewrite the intercepts in terms of points.

X-intercept of 1: .

Y-intercept of 2:

Write the slope-intercept form for linear equations.

Substititute the y-intercept into the slope-intercept equation.

Substitute both the x-intercept point and the y-intercept into the equation to solve for slope.

Rewrite by substituting the values of and into the y-intercept form.

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Question

Which equation has a y-intercept at 2 and x-intercepts at -1 and 6?

Answer

In order for the equation to have x-intercepts at -1 and 6, it must have and as factors. This leaves us with only 2 choices, or

This equation must also have a y-intercept of 2. This means that plugging in 0 for x will gives us a y-value of 2. Because we have two options, we could plug in 0 for x in each to see which gives us an answer of 2:

a) we can eliminate that choice

b) this must be the right choice.

If we hadn't been given multiple options, we could have set up the following equation to figure out the third factor:

divide by -6

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Question

Which equation would have an x-intercept at and a y-intercept at ?

Answer

We're writing the equation for a line passing through the points and . Since we already know the y-intercept, we can figure out the slope of this line and then write a slope-intercept equation.

To determine the slope, divide the change in y by the change in x:

The equation for this line would be .

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Question

Write the equation of a line with intercepts and

Answer

The line will eventually be in the form where is the y-intercept.

The y-intercept in this case is .

To find the equation, plug in for , and the other point, as x and y:

add to both sides

This means the equation is

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Question

Which equation has the x- and y-intercepts and ?

Answer

Since this line has the y-intercept , we know that in the form ,

We can plug in the other intercept's coordinates for and to solve for :

subtract

divide by

The line is

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