Tutor.com Quadratic Equations Session

Sep. 20, 2012

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Session Transcript - Math - Algebra, 5/31/2012 6:38PM - Tutor.comSession Date: 5/31/2012 6:38PM
Length: 23.4 minute(s)
Subject: Math - Algebra


System Message
[00:00:00] *** Please note: All sessions are recorded for quality control. ***

Guest (Customer)
[00:00:00] solving quadratic equations

Melissa C (Tutor)
[00:00:07] hi welcome to tutor.com
[00:00:14] how can i help you today

Guest (Customer)
[00:00:14] hello
[00:00:25] let me type my question

Melissa C (Tutor)
[00:00:30] ok

Guest (Customer)
[00:00:34] pls give me a second thank you very much

Melissa C (Tutor)
[00:00:59] no problem

Guest (Customer)
[00:01:46] the problem is :
[00:02:35] Y = -x^2- 2x + 1

Melissa C (Tutor)
[00:02:41] ok

Guest (Customer)
[00:02:44] can you help me with that?

Melissa C (Tutor)
[00:02:53] sure

Guest (Customer)
[00:02:55] step by step ple
[00:02:56] ase

Melissa C (Tutor)
[00:03:02] what are you being asked to do with this?

Guest (Customer)
[00:03:36] complete the square and graph it. i am not sure how

Melissa C (Tutor)
[00:03:51] aah ok
[00:04:09] well lets write it on the board
[00:04:18] would you like to do that?

Guest (Customer)
[00:04:22] ok
[00:04:25] thank you

Melissa C (Tutor)
[00:04:28] sure

Guest (Customer)
[00:04:44] please explain it in super detail. i don't know how.

Melissa C (Tutor)
[00:04:51] its ok
[00:04:57] these can be difficult

Guest (Customer)
[00:06:07] it's funny that i got tested on the may 29th in my college and i was eligible for math 191 (calculus) but i got this one wrong . i forgot how to do it

Melissa C (Tutor)
[00:06:21] its ok
[00:06:49] you actually wont do a lot of this in calc - it's a good skill to have bc it helps you understand manipulating an equation
[00:07:01] but its not a skill we use alot
[00:07:15] specifically completing the square i mean

Guest (Customer)
[00:07:41] yes. i know. i have quite a good grip on calculus but somehow i forgot how to do this one. yes, i learned this in primary school in china. thats why i forgot maybe

Melissa C (Tutor)
[00:08:05] aaah - yes sometimes it's hard to go back to the basics
[00:08:14] so onward to the problem

Guest (Customer)
[00:08:21] yes mam

Melissa C (Tutor)
[00:08:25]
[00:09:51] are you able to write the equation on the board?
[00:09:56] aah k
[00:10:04] well actually
[00:10:40] i would move that -1 in front of the x^2 first
[00:10:56] i can do this by dividing everything by -1

Guest (Customer)
[00:11:14] hm...im sorry... why should i divide it by 1?

Melissa C (Tutor)
[00:11:35] b -1
[00:11:38] by -1
[00:11:46] it makes working with the x^2 easier
[00:12:41] anytime you have a coefficient in front of x^2, esp if it is not a perfect square itself
[00:12:46] consider this step first

Guest (Customer)
[00:12:55] so -Y = X^2 + 2x - 1

Melissa C (Tutor)
[00:13:00] right
[00:13:24] now you are correct in moving the -1 to the other side because it does not complete the square
[00:13:54] to complete the square,

Guest (Customer)
[00:14:17] im so soorrryyy i still dont remember why do you need to plus 1

Melissa C (Tutor)
[00:14:36] its ok
[00:14:41] to complete th square

Guest (Customer)
[00:14:57] but how o you know to add 1? not other numbers?

Melissa C (Tutor)
[00:15:09] you only move the constant out of the way
[00:15:19] you need the other 2 parts to complete the square
[00:15:32] do you remember what a perfect square trinomial is?

Guest (Customer)
[00:15:44] no :'(

Melissa C (Tutor)
[00:15:47] its ok

Guest (Customer)
[00:16:08] ohhhh yes yes yes

Melissa C (Tutor)
[00:16:20] great
[00:16:37] now what we are missing from the right side is the b^2 piece

Guest (Customer)
[00:16:51] yes

Melissa C (Tutor)
[00:16:54] to figure out what to add
[00:17:01] we take the middle term
[00:17:11] the x term
[00:17:17] divide the number in half

Guest (Customer)
[00:17:17] ok and then

Melissa C (Tutor)
[00:17:20] and

Guest (Customer)
[00:17:45] the middle term divided by HALF!!!!
[00:17:54] ah yes now i remember!!! )))))))

Melissa C (Tutor)
[00:17:55] and then square it

Guest (Customer)
[00:18:10] =1

Melissa C (Tutor)
[00:18:15] right
[00:18:17] BUT

Guest (Customer)
[00:18:21] awwwww yeahhhhhhhhhh

Melissa C (Tutor)
[00:18:22] whatever you add to one side
[00:18:26] hahaha

Guest (Customer)
[00:18:28] ok thank you very much!

Melissa C (Tutor)
[00:18:47] sure

Guest (Customer)
[00:18:50] aahhh yeaaahhhhh

Melissa C (Tutor)
[00:19:08] next step is to simplify

Guest (Customer)
[00:19:48] so the answer is (-1, 2 )

Melissa C (Tutor)
[00:20:11] yup

Guest (Customer)
[00:20:29] constant is -1 < 0 therefore it will open downward because it is negative constant

Melissa C (Tutor)
[00:20:40] exactly
[00:20:58] i would probably redivide by -1 to move it back to the right side
[00:21:21] and boom
[00:21:24] there ya go
[00:22:15] well the neg 1 is actually from inside the ()

Guest (Customer)
[00:22:21] ma bad
[00:22:25] ok

Melissa C (Tutor)
[00:22:29] the outside neg 1 is the one the says up or down
[00:22:31] yup
[00:22:46] so i hope this has helped refresh your memory

Guest (Customer)
[00:22:55] ok i get it. thank you
[00:22:57] bye bye

Melissa C (Tutor)
[00:23:04] sure no problem = good luck with calc

Guest (Customer)
[00:23:11] yes OF COURSE it helps!
[00:23:13] thank you

Melissa C (Tutor)
[00:23:19]