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Sat Oct 13, 2012 5:09 am
Forum: Calculus
Topic: Implicit differentiation with tan: dy/dx for tan(xy)
Replies: 2
Views: 13289

### Re: Implicit differentiation with tan: dy/dx for tan(xy)

What would dy/dx of tan(xy) be using implicit differentiation be?
$\frac{d}{dx}\tan(xy)=\sec^2(xy)\cdot (y+xy')$
Sat Oct 13, 2012 5:06 am
Forum: Pre-Algebra
Topic: Distributive Property
Replies: 3
Views: 6990

### Re: Distributive Property

I am lost when I reach the line in red: (–4) + (5x – x) + (7y – y) simplification (23 – 27 = –4) (–4) + x(5 – 1) + y(7 – 1) Distributive Property Where did that (1) come from, please? Check it by re-distributing the x and y: (-4) + x(5 - 1) + y(7 - 1) (-4) + (x*5 - x*1) + (y*7 - y*1) (-4) + (5x - x...
Sat Oct 13, 2012 5:02 am
Forum: Calculus
Topic: Increasing/Decreasing intervals for Trig
Replies: 6
Views: 8717

### Re: Increasing/Decreasing intervals for Trig

f(x) = 20x - 10\sin(4x) f'(x)=20-40\cos(4x)=0 \cos(4x)=\frac12 4x=\pm\frac{\pi}{3}+2\pi n x=\pm\frac{\pi}{12}+\frac{n\pi}{2} f is increasing on intervals of the form: [\frac{\pi}{12}+\frac{n\pi}{2},-\frac{\pi}{12}+\frac{(n+1)\pi}{2}] f is decreasing on intervals of the form: [-\frac{\pi}{12}+\frac{...
Sun Sep 23, 2012 1:36 am
Forum: Intermediate Algebra
Topic: Can you explain how to do this?
Replies: 2
Views: 2118

### Re: Can you explain how to do this?

Multiply each term by (x-2)(x+2). Cancel factors which the numerator and denominator have in common: \frac{x}{x-2}-\frac{1}{x+2}=1 \frac{x}{x-2}\times\frac{(x-2)(x+2)}{1}-\frac{1}{x+2}\times\frac{(x-2)(x+2)}{1}=1\times\frac{(x-2)(x+2)}{1} x(x+2)-(x-2)=(x-2)(x+2) The rest is history: x^2+2x-x+2=x^2-4...
Fri Sep 21, 2012 4:02 am
Forum: Forum Rules & Guides
Topic: url tags
Replies: 2
Views: 6931

### Re: url tags

It looks like it's working now:

WolframAlpha calculation

Previously, I received an error message which said I that the url tags were turned off.
Maybe a mechanism to keep spammers away?
Wed Sep 19, 2012 9:43 pm
Forum: Forum Rules & Guides
Topic: url tags
Replies: 2
Views: 6931

### url tags

How come I can't use the BBCode url tags?
I see that other members can.

Wed Sep 19, 2012 9:41 pm
Forum: Intermediate Algebra
Topic: Solving a system of two eqn's.
Replies: 3
Views: 2004

### Re: Solving a system of two eqn's.

You can always check your answers using WolframAlpha:

http://goo.gl/lRNOV

This matches MrAlgebra's answer.
Sun Sep 16, 2012 11:21 pm
Forum: Beginning Algebra
Topic: Algebra: writing equation describing max, min temperature
Replies: 1
Views: 5028

### Re: Algebra

Maximum:
x = 200 + 5
x = 205 (degrees Fahrenheit)

Minimum:
x = 200 - 5
x = 195 (degrees Fahrenheit)
Sun Sep 16, 2012 11:16 pm
Forum: Beginning Algebra
Topic: Fractional Algebriac Equation help!!
Replies: 1
Views: 2007

### Re: Fractional Algebriac Equation help!!

Hi Lotrnerd,

Minor mistake here:

a + a/2 + (a/2)/2 + 3[(a/2)/2] = 180
a + a/2 + (a/2 * 1/2) + 3((a/2) * (1/2)) = 180
a + a/2 + a/4 + 3a/4 = 180

Here you have to multiply by 4 to clear the fractions:

4a + 2a + a + 3a = 720
10a = 720
a = 72
Tue May 19, 2009 9:47 pm
Forum: Matrix (Linear) Algebra
Topic: find basis for (a-2b+5c,2a+5b-8c,-a-4b+7c,3a+b+c)
Replies: 8
Views: 12055

### Re: find basis for (a-2b+5c,2a+5b-8c,-a-4b+7c,3a+b+c)

$(a-2b+5c,2a+5b-8c,-a-4b+7c,3a+b+c)=a(1,2,-1,3)+b(-2,5,-4,1)+c(5,-8,7,1)$

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