3.5 write and graph equations of lines
21
3.5 3.5 Write and Graph Equations of Lines Bell Thinger 1. If 2x + 5y = –20 and x = 0, what is y? ANSWER –4 What is the slope of the line containing the point , 7) and (3, –10)? ANSWER –17 3. Orphelia bought x apples. If each apple costs $.59, write an equation for y, the total cost of x apples. ANSWER y = 0.59x
-
Upload
detwilerr -
Category
Technology
-
view
901 -
download
2
Transcript of 3.5 write and graph equations of lines
3.53.5 Write and Graph Equations of LinesBell Thinger
1. If 2x + 5y = –20 and x = 0, what is y?
ANSWER –4
2. What is the slope of the line containing the points (2, 7) and (3, –10)?
ANSWER –17
3. Orphelia bought x apples. If each apple costs $.59, write an equation for y, the total cost of x apples.
ANSWER y = 0.59x
3.5
3.5Example 1
SOLUTION
m4 – (– 2)
0 – 3 = 6
– 3= = – 2
STEP 2 Find the y-intercept. The line intersects the y-axis at the point (0, 4), so the y-intercept is 4.
STEP 1 Find the slope. Choose two points on the graph of the line, (0, 4) and (3, –2).
Write an equation of the line in slope- intercept form.
STEP 3 Write the equation.
y = –2x + 4
mx + by = Use slope-intercept form.
Substitute – 2 for m and 4 for b.
3.5Example 2Write an equation of the line passing through the point (– 1, 1) that is parallel to the line with the equation y = 2x – 3.
SOLUTION
STEP 1 Find the slope m. The slope of a line parallel to y = 2x –3 is the same as the given line, so the slope is 2.
STEP 2 Find the y-intercept b by using m = 2 and (x, y) = (– 1, 1).
y mx + b=
1 = 2 (–1 ) + b
3 = b
Use slope-intercept form.
Substitute for x, y, and m.
Solve for b.
Because m = 2 and b = 3, an equation of the line is y = 2x + 3.
3.5Example 3Write an equation of the line j passing through the point (2, 3) that is perpendicular to the line k with the equation y = – 2x + 2.
SOLUTIONSTEP 1 Find the slope m of line j. Line k has a slope of – 2.
12
m =
The product of the slopes of lines is – 1.
Divide each side by – 2.
mx + by =
3 = 12
( 2 ) + b
2 = b
Use slope-intercept form.
Substitute for x, y, and m.
Solve for b.
STEP 2 Find the y-intercept b by using m = and (x, y) = (2, 3).
12
– 2 m = – 1
3.5Example 3Because m = and b = 2, an equation of line j is
y = x + 2. You can check that the lines j and k
are perpendicular by graphing, then using a protractor to measure one of the angles formed by the lines.
21
21
3.5Guided Practice
Write an equation of the line in the graph at the right.
1.
y = – 1 2 3
xANSWER
Write an equation of the line that passes through (– 2, 5) and (1, 2).
2.
ANSWER y = –x + 3
3.5Guided PracticeWrite an equation of the line that passes through the point (1, 5) and is parallel to the line with the equation 6x – 2y = 10. Graph the lines to check that they are parallel.
3.
ANSWER y = 3x + 2
3.5Guided Practice
How do you know the lines x = 4 and y = 2 are perpendicular?
4.
x = 4 is a vertical line while y = 2 is a horizontal line.
SAMPLE ANSWER
3.5Example 4Gym Membership
The graph models the total cost of joining a gym. Write an equation of the line. Explain the meaning of the slope and the y-intercept of the line.
SOLUTION
Find the slope.STEP 1
= 44m =363 – 231
5 – 2
132 3=
3.5Example 4
STEP 2 Find the y-intercept. Use the slope and one of the points on the graph.
mx + by =
143 = b
Use slope-intercept form.
Substitute for x, y, and m.
Simplify.
STEP 3 Write the equation.
Because m = 44 and b = 143, an equation of the line is y = 44x + 143.
The equation y = 44x + 143 models the cost. The slope is the monthly fee, $44, and the y-intercept is the initial cost to join the gym, $143.
44 2 + b231 =
3.5
3.5Example 5Graph 3x + 4y = 12.
SOLUTION
The equation is in standard form, so you can use the intercepts.
STEP 1 Find the intercepts.
To find the x-intercept, let y = 0.
3x + 4y = 12
3x +4 ( 0 ) = 12
x = 4
To find the y-intercept, let x = 0.
3x + 4y = 12
3 ( 0 ) + 4y = 12
y = 3
3.5Example 5STEP 2 Graph the line.
The intercepts are (4, 0) and (0, 3). Graph these points, then draw a line through the points.
3.5Guided Practice
6. 2x – 3y = 6
Graph the equation.
ANSWER
3.5Guided Practice
Graph the equation.
7. y = 4
ANSWER
3.5Guided Practice
Graph the equation.8. x = – 3
ANSWER
3.5Example 6
SOLUTION
STEP 1
Model each rental with an equation.
Cost of one month’s rental online: y = 15
Cost of one month’s rental locally: y = 4x, where x represents the number of DVDs rented
DVD RentalYou can rent DVDs at a local store for $4.00 each. An Internet company offers a flat fee of $15.00 per month for as many rentals as you want. How many DVDs do you need to rent to make the online rental a better buy?
3.5Example 6Graph each equation.STEP 2
The point of intersection is (3.75, 15). Using the graph, you can see that it is cheaper to rent locally if you rent 3 or fewer DVDs per month. If you rent 4 or more DVDs per month, it is cheaper to rent online.
3.5Exit Slip
y = x – 1 ANSWER 43
2. Write an equation of the line that passes through the point (4, –2) and has slope 3.
y = 3x – 14ANSWER3. Write an equation of the line that passes through
the point (7, 1) and is parallel to the line with equation x = 4. x = 7ANSWER
1. Write an equation of line that has slope and y-intercept – 1.
43
4. Write an equation of the line that passes through the point (7, 1) and is perpendicular to the line with equation 6x – 3y = 8.
y = – x +ANSWER21
29
3.5
Homework
Pg 190-193#5, 20, 26, 39, 63
![X } X µ l W o } v } Á ] } v Z ] Z D Z P v ] X } X µ l - Maths Genie · 2019. 7. 23. · Two of these lines are parallel. Write down the two parallel lines. Here are the equations](https://static.fdocument.pub/doc/165x107/5fde06ee05260f257a507978/x-x-l-w-o-v-v-z-z-d-z-p-v-x-x-l-maths-genie-2019-7.jpg)
