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by testing
Mon Jun 29, 2009 5:04 pm
Forum: Matrix (Linear) Algebra
Topic: given system, find solns, show solns form vector space, and
Replies: 1
Views: 2846

given system, find solns, show solns form vector space, and

I need to find the set of solutions to a system of linear equations, show that they are a vector space of R^4, and find a basis for them. The equations are: x 1 - 2x 3 - 3x 4 = 0 x 2 - 3x 3 + x 4 = 0 2x 1 - x 2 - x 3 - 7x 4 = 0 I got a solution of x = x 3 *(2, 3, 1, 0). I could show closure, but how...
by testing
Mon May 18, 2009 8:11 pm
Forum: Discrete Math
Topic: need to find the median from frequency table??
Replies: 1
Views: 2309

Re: need to find the median from frequency table??

There are 2+3+7+5+3=20 points, so the median is the average of the 10th & 11th. But you have classes, not the actual points, so you have to start at the bottom of the interval (10-14, probably 9.5). The 10th point is 5th (of 7) in the interval & the interval is 5 wide, so its 9.5+(5/7)(5).
by testing
Wed Mar 25, 2009 7:46 pm
Forum: Matrix (Linear) Algebra
Topic: A, B, and C are 2 x 2 matrices. Solve eqn for C: B=(BC+2A)
Replies: 1
Views: 2014

A, B, and C are 2 x 2 matrices. Solve eqn for C: B=(BC+2A)

A, B, and C are 2 x 2 matrices. Solve the equation for C: B=(BC+2A)

My quess is this: C=inv(A)-(2A)(inv(B)), but I am not sure...that is whay I am writing you.

Thank you for your time
by testing
Mon Mar 23, 2009 6:24 pm
Forum: Advanced Algebra ("pre-calculus")
Topic: value of sqrt(2sqrt(2sqrt(...))) (I'm told there's a trick?)
Replies: 3
Views: 3399

Okay, I never would have thought of that. :shock:
by testing
Sun Mar 22, 2009 4:15 pm
Forum: Advanced Algebra ("pre-calculus")
Topic: value of sqrt(2sqrt(2sqrt(...))) (I'm told there's a trick?)
Replies: 3
Views: 3399

value of sqrt(2sqrt(2sqrt(...))) (I'm told there's a trick?)

I'm trying to find the value of sqrt(2sqrt(2sqrt(...))). I figure you start by setting this equal to "x". But then what?

I'm told there's a trick to this, so maybe that's why I'm stuck?

Edited to correct misunderstanding of original puzzle.
by testing
Fri Mar 20, 2009 1:26 pm
Forum: Matrix (Linear) Algebra
Topic: find values for a, b, and c for which matrix A is symmetric
Replies: 1
Views: 4126

find values for a, b, and c for which matrix A is symmetric

find values for a, b, and c for which the matrix A is symmetric

matrix A =   2   a-2b+c   2a+b+c
3 5 a+c
0 -2 7


i know that a-2b+c=3 and son on ... but i cant seem to process the equation to get answers consistent for the equation.
by testing
Wed Mar 04, 2009 7:41 pm
Forum: Matrix (Linear) Algebra
Topic: Matrix A where system Ax = b solvable, but not nec. uniquely
Replies: 1
Views: 2316

Matrix A where system Ax = b solvable, but not nec. uniquely

Give an example of a matrix A for which the system Ax= b can be solved for any b, but not necessarily uniquely.

Is there a way to do this that does not involve "brute force"?
by testing
Sun Mar 01, 2009 7:15 pm
Forum: Matrix (Linear) Algebra
Topic: For 2-by-2 matrix A, show that det(sA) = s^2 * det(A)
Replies: 2
Views: 2330

For 2-by-2 matrix A, show that det(sA) = s^2 * det(A)

Let A be any 2-by-2 matrix, and let s be any real-valued scalar. Show that det (sA) = s 2 * det (A). A = [ a b ] sA = [ sa sb ] [ c d ] [ sc sd ] det(A) = ad - cb det(sA) = (sa)(sd) - (sc)(sb) = s^2(ad) - s^2(cb) = s^2 * det(A)...

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