HP 15c User Manual

Page 183

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Section 13: Finding the Roots of an Equation 183

Keystrokes

Display

´_ 0

5.0000

The desired root.

After the routine finds and displays the root, you can ensure that the
displayed number is indeed a root of f(x) = 0 by checking the stack. You have
seen that the display (X-register) contains the desired root. The Y-register
contains a previous estimate of the root, which should be very close to the
displayed root. The Z-register contains the value of your function
evaluated at the displayed root.

Keystrokes

Display

)

5.0000

A previous estimate of the
root.

)

0.0000

Value of the function at the
root showing that f(x) = 0.

Quadratic equations, such as the one you are solving, can have two roots. If
you specify two new initial estimates, you can check for a second root. Try
estimates of 0 and -10 to look for a negative root.

Keystrokes

Display

0

v

0.0000

Initial estimates.

10

–10

´ _ 0

–2.0000

The second root.

)

–2.0000

A previous estimate of the
root.

)

0.0000

Value of f(x) at second root.

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