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Old 01-12-2014, 03:17 PM
 
Location: Elsewhere
88,527 posts, read 84,719,546 times
Reputation: 115010

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Quote:
Originally Posted by GeorgiaTransplant View Post
S = B +10

S + 1 = 2(B+1)
S + 1 = 2B + 2
S = 2B+1

B + 10 = 2B + 1

B = 9

S = 9 + 10

Billy is 9, Suzy is 19
This is what I'm talking about! I figured out the answer in about five seconds just using logic, but I wouldn't know how to do the algebra problem above, which certainly took longer than it takes to figure it out just using logic.

If she's ten years older than he is, the only possible time she's going to be twice as old as he is is when she's 20. So she's 19 now. And it takes longer to type that than it does to figure it out.
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Old 01-12-2014, 04:56 PM
 
Location: Viña del Mar, Chile
16,391 posts, read 30,922,186 times
Reputation: 16643
Quote:
Originally Posted by Longhornsfan87 View Post
How practical is algebra in the real world? When will you ever have to solve for X?
This cannot be serious.
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Old 01-13-2014, 05:25 PM
 
13,395 posts, read 13,500,225 times
Reputation: 35712
Quote:
Originally Posted by Mightyqueen801 View Post
This is what I'm talking about! I figured out the answer in about five seconds just using logic, but I wouldn't know how to do the algebra problem above, which certainly took longer than it takes to figure it out just using logic.

If she's ten years older than he is, the only possible time she's going to be twice as old as he is is when she's 20. So she's 19 now. And it takes longer to type that than it does to figure it out.
What you're calling "logic" is really algebra. If someone asked you how did you get that answer, what would you tell them? You have to be able to explain your "logic."

How would you teach this "logic?"

Also, that problem was fairly easy and used nice even numbers.
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Old 01-13-2014, 05:54 PM
 
Location: Northville, MI
11,879 posts, read 14,202,675 times
Reputation: 6376
Quote:
Originally Posted by charlygal View Post
Here's today's algebra problem. Any takers? Show your work.

Suzy is ten years older than Billy, and next year she will be twice as old as Billy. How old are they now?
Take Billy's age as x

Suzy's age as y

This year

y=x+10

Next year

y+1=2*(x+1)

Substituting for y we have

2*x+2=x+10+1

2*x+2=x+11

x=9=Billy's age

y=19=Suzy's age

This year Billy is 9 and Suzy is 19 (criteria 1 is met)

Next year Billy is 10 and Suzy is 20 (criteria 2 is met).
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Old 01-13-2014, 06:03 PM
 
Location: Northville, MI
11,879 posts, read 14,202,675 times
Reputation: 6376
Now solve this guys. Use those thinking caps :

Two roots of a 4th degree equation x^4 +12x^3+27x^2+42x+56 are given as 2+-i. Find the other two roots.

Show all your work.
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Old 01-13-2014, 06:15 PM
 
Location: Richmond, VA
5,047 posts, read 6,345,715 times
Reputation: 7204
Quote:
Originally Posted by Adi from the Brunswicks View Post
Now solve this guys. Use those thinking caps :

Two roots of a 4th degree equation x^4 +12x^3+27x^2+42x+56 are given as 2+-i. Find the other two roots.

Show all your work.
D = X^4
O = 12x^3
Y = 27x^2
O = 12x^3
U = 42X
R = 56
O = 12x^3
W = 2 + i
N = 2 - i
H = Integral of X^4
O = 12x^3
M = Integral of 12x^3
E = Integral of 27x^2
W = 2 + i
O = 12x^3
R = 56
K = Integral of 42X

Read the substituted variables straight down the left and you'll have your answer.
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Old 01-13-2014, 06:27 PM
 
Location: So Ca
26,719 posts, read 26,787,779 times
Reputation: 24785
Quote:
Originally Posted by Mightyqueen801 View Post
I figured out the answer in about five seconds just using logic, but I wouldn't know how to do the algebra problem above, which certainly took longer than it takes to figure it out just using logic.
You would excel with Common Core!
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Old 01-13-2014, 06:44 PM
 
Location: Northville, MI
11,879 posts, read 14,202,675 times
Reputation: 6376
Quote:
Originally Posted by GeorgiaTransplant View Post
D = X^4
O = 12x^3
Y = 27x^2
O = 12x^3
U = 42X
R = 56
O = 12x^3
W = 2 + i
N = 2 - i
H = Integral of X^4
O = 12x^3
M = Integral of 12x^3
E = Integral of 27x^2
W = 2 + i
O = 12x^3
R = 56
K = Integral of 42X

Read the substituted variables straight down the left and you'll have your answer.
Dude, I did this 4 years ago in 11th Grade . I know how to approach it. Just asked this to get folks thinking. But here is the solution anyways. I highlighted the key steps:

Sum of the roots=(2+i)+(2-i)=4
Product of the roots=(2+i)*(2-i)=4-(i)^2=4-1=3

Quadratic equation 1=x^2+4x+3


Assume Quadratic equation 2=ax^2+bx+c

Multiplying we have

(ax^2+bx+c)*(x^2+4x+3)=x^4 +12x^3+27x^2+42x+56

Comparing coefficients:
x^4----a=1
x^3----4a+b=12 therefore b=8
x^2----3a+4b+c=27 therefore c=27-32-3=-8

Hence, we need to solve x^2+8x-8=0 to obtain the other 2 roots

Making use of the quadratic formula

x=(-8+-(64+32)^1/2)/2=(-8+-(96)^1/2)/2=-4+-2(6)^1/2

Other 2 roots are real:
x=-4+2(6)^1/2
(or)
x=-4-2(6)^1/2


I would love giving these problems on High school final exams. Actually prepares kids for college by mandating them to think through the solution procedure instead of BS through .
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Old 01-13-2014, 06:46 PM
 
50 posts, read 58,314 times
Reputation: 103
Anything algebra 2 and higher is pretty useless for most people. You're most likely never going to use quadratic equations or anything like that during your lifetime.
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Old 01-13-2014, 06:51 PM
 
Location: Northville, MI
11,879 posts, read 14,202,675 times
Reputation: 6376
Quote:
Originally Posted by LookingtoleaveFL View Post
Anything algebra 2 and higher is pretty useless for most people. You're most likely never going to use quadratic equations or anything like that during your lifetime.
No its not. Tell that the next time a plane crash occurs due to controls failure.

Control system design involves deep knowledge in complex algebra and differential equations.

Last edited by Adi from the Brunswicks; 01-13-2014 at 07:11 PM..
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