Using graphing technology, approximate where the graph of y = 5x2 − 3x − 9 crosses the x-axis.

(1.55, 0) and (−1.15, 0)
(1.23, 0) and (−1.26, 0)
(1.32, 0) and (−1.01, 0)
(1.68, 0) and (−1.08, 0)

Question

Using graphing technology, approximate where the graph of y = 5x2 − 3x − 9 crosses the x-axis.
 	
	(1.55, 0) and (−1.15, 0)
	(1.23, 0) and (−1.26, 0)
	(1.32, 0) and (−1.01, 0)
	(1.68, 0) and (−1.08, 0)

agreene · Answer

http://www4b.wolframalpha.com/Calculate/MSP/MSP36651a0ih2e3e00ef77c00001h1b699b9c870593?MSPStoreType=image/gif&s=57&w=399&h=185&cdf=RangeControl

anonymous · Answer

Quadratic formula...
a=5
b=-3
c=-9

Plug them in and you'll get two answers for x.  Both y-values will be 0.

anonymous · Answer

Or do you want me to tell you how to do this on a TI-83/84?

anonymous · Answer

I have no idea how to do any of these..:/

anonymous · Answer

Do you have a graphing calculator?

anonymous · Answer

Nope...

agreene · Answer

the link I put is a picture of the graph--you can use it to do the estimation they are asking for.

anonymous · Answer

http://0.tqn.com/d/create/1/0/i/9/9/-/Quadratic.formula.jpg

anonymous · Answer

a=5
b=-3
c=-9

Plug them in and you'll get two answers for x.  Both y-values will be 0.

anonymous · Answer

(-(-3) +/- sqrt((-3)^2 - 4*5*(-9)))/(2*5)

anonymous · Answer

(3 +/- (sqrt(9+180))/10

(3+/- sqrt(189))/10

***THIS MEANS***

x = (3+ sqrt(189))/10

y=0

x = (3-sqrt(189))/10

y=0

Is this making sense?