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Texas Instruments TI-85 User Manual

Page 15

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Chapter 1

B-15

Copyright © Houghton Mifflin Company. All rights reserved.

Press

F4

(

TRACE

) and use

and/or

to move

along the graph of the equation in

y

1

.

Press

to jump from the graph of

y

1

to the graph of

y

2

. Tracing reveals that guesses for the input values

where these two graph intersect are

x

»

10.6

,

x

»

3.8

.

Return to the home screen with

2nd

EXIT

(

QUIT

) .

Access the

SOLVER

and enter the equation

y

1

=

y

2

as shown on the right. Enter the guess for the left-
most intersection point and solve for x.

Enter the guess for the rightmost intersection point
and solve for x.

The two solutions to the equation, reported to four
decimal places, are x =

10.5774 and x = 3.7462.

1.2.3 GRAPHICALLY FINDING INTERCEPTS

Finding where a function graph crosses

the vertical and horizontal axis can be done graphically as well as by the methods
indicated in 1.2.2 of this Guide. Remember the process by which we find intercepts:

¥ To find the y-intercept of a function y = f(x), set x=0 and solve the resulting equation.

¥ To find the x-intercept of a function y = f(x), set y=0 and solve the resulting equation.

Also remember that an x-intercept of a function y = f(x) has the same value as the root or
solution of the equation f(x) = 0.

Clear all locations in the

y(x)=

list and enter in

y

1

f(x) = 4x Ð x

2

Ð 2.

Draw a graph with

F3

(

ZOOM

)

MORE

F4

(

ZDECM

) . Press

F2

(

RANGE

or

WIND

) and reset

yMin

to -

6

for a

good view of all intercepts. Press

F5

(

GRAPH

) .

Even though it is very easy to find f(0) =

2, you can

have the calculator find the y-intercept while view-
ing the graph by pressing

TI-85

MORE

F1

(

MATH

)

MORE

F4

(

YICPT

)

TI-86

MORE

F1

(

MATH

)

MORE

F2

(

YICPT

)

Both

View the y-intercept f(0) =

2.