Do Now:
• What do you know about the following:– Slope– x-intercept, y-intercept– Linear equations– Calculus
Lines
Increments
• Calculus has proven to be useful for relating the rate of change of a quantity to the graph of the quantity.
• In order to begin explaining this relationship we must begin with the slopes of lines.
Increments
• When a particle in the plane moves from one point to another we must use the starting point and stopping point to discuss change.
Increments
• If a particle moves from point (x1,y1) to the point (x2,y2), the increments in its coordinates are:
x = x2 – x1 and y = y2 – y1
Increments
Let a particle move from P1(x1, y1) to P2(x2, y2). The increments in its coordinates are x = (x2 – x1) and y= (y2 – y1).
Ex. The coordinate increments from (4, -3) to (2, 5) are:
Solutionx = (x2 – x1) = 2 – 4 = -2 and y = (y2 – y1) = 5- -3 = 8.
Ex. The coordinate increments from (5, 6) to (5, 1) are:
Solution
x = (x2 – x1) = 5 – 5 = 0 and y = (y2 – y1) = 1- 6 = -5.
Slope
• Each nonvertical line has a slope, and we can use increments to calculate our slope.
Slope
• Let P1(x1, y1) and P2(x2, y2) be points on a nonvertical line, L. The slope of L is
12
12
xx
yy
x
y
run
risem
PARALLEL PERPENDICULAR
Parallel and Perpendicular lines
m1 = m2
Equations of vertical & horizontal lines
Ex. Find the equations of the vertical and horizontal lines that pass through the point (2, 3)
Solution
(2, 3)Y = 3
x = 2
Point-slope Equation
The equation y - y1 = m(x –x1) is the point slope formula with m = slope and (x1, y1) is a pt on line
Ex. Find the equation of the line that passes through (-1, 2) and is
a)Parallel to y = 3x – 4
b)Perpendicular to y = 3x - 4
Solutiona)y – 2 = 3(x - -1) => y = 3x + 5
b) Y – 2 = (-1/3)*(x - -1) => y = -x/3 + 5/3
Slope-intercept Equation
The equation y = mx + b is the slope-intercept formula with m = slope and b = y-intercept
Ex. Find the equation of the line through (-1, 2) that passes through (0, 5).
Solution
m = (5 – 2)/(0 - –1) => m = 3. Since (0, 5) is the y-intercept, we get y = 3x + 5.
General Linear Equation
The equation Ax + By = C (A and B not both 0) is the general linear equation.
Solution
Sketch the line 8x + 5y = 40
Substitute x = 0 => y = 8; substitute y = 0 => x = 5.
X
Y
X
5
X8
Using the best fitting line to predict future trends
Linear Regression
Year Population (mil)
1986 4936
1987 5023
1988 5111
1989 5201
1990 5329
1991 5422
Ex Use a linear model of the data in the table to predict the population in the year 2010.
Method 1
Draw a scatter plot by hand and overlap the best fitting straight line.
4900
5000
5100
5200
5300
5400
5500
1984 1986 1988 1990 1992
Best fit
Method 1, continued
Find the equation of the line and use its equation to predict population in 2010.
Eqn: Use point slope formula. Use 2 pts on best line.
(1986, 4936mil), (1990, 5300mil)
m = (5300-4936)/(1990-1986) = 364/4 = 91 (mil/yr)
y – 4936mil = 91mil(x – 1986)
y = 91mil*x - 175790mil.
In 2010, the population will be 91(2010) – 175790
Pop = 7120 mil <= INACCURATE
Method 2
Use the capabilities of the TI-89 calculator.
To simplify, let x = 0 represent 1986, x = 1 represent 1987 etc.
{0, 1, 2, 3, 4, 5} -> L1 ENTER
2nd { 0, 1, 2, 3, 4, 5 2nd }
STO alpha L 1
ENTER(Upper case L used for clarity.)
Method 2, continued
{4936, 5023, 5111, 5201, 5329, 5422} -> L2 ENTER
2nd { 4936, 5023, 5111, 5201, 5329, 5422 2nd }
STO alpha L 2
ENTER(Upper case L used for clarity.)
2nd MATH 6 3 2
LinReg
alpha L 1 alpha L 2 ENTER
DoneThe calculator should return:
,
LinReg L1, L2 ENTER
Statistics Regressions
Method 2, continued
ShowStat ENTER
2nd MATH 6 8
Statistics ShowStat
ENTER
The calculator gives you an equation and constants:
y = ax + b
a = 98.228571, b = 4924.761905, corr = 0.997826
R2 = 0.995658
Method 2, continued
Use calculator - plot new curve & the original points:
Y= y1=regeq(x)
2nd VAR-LINK regeq
x )
Plot 1 ENTER
ENTER
WINDOW
Use alpha etc. Type in L1 and L2
Method 2, continued
WINDOW Xmin = 0
Xmax = 5
Xsc = 1
Ymin = 4936
Ymax = 5422
Ysc = 1
Xres = 1
GRAPH produces the graph
Method 2, continued
Go to the homescreen
2nd QUIT
To get the population in 2010, note that 2010 is 24 years after 1986. So we enter y1(24) at homescreen and obtain 7282.25 (mil).
Compare this value with the value obtained using the “by hand” method
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