Math Is Fun Forum

capecodder

Member

Registered: 2010-09-26

Posts: 1

algebra

what natural number is 5 times the sum of its digits?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: algebra

Hi capecodder;

Welcome to the forum!

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Kilo123

Member

Registered: 2010-10-04

Posts: 2

Re: algebra

Can anyone determine what this question is asking? I am doing challenge problems and literally cannot even determine what it is asking. Okay.     y=1/(x+1)                     Let x_0=/= -1 Find equation of tangent line at x=x_0
Simple d/dx= -1/(x+1)^2
Equation y= -(1/x_0+1)^2)x+y_0

next part: what point on the curve does the tangent line have the same slope as x=x_0 ????
Find the equation of the secant at x=x_1 and x=x_2

I have simply y-y_0=(change in y/x_2-x_2)(x-x_1)

and then the last part is way over my head in the fact that i dont even know what it is asking

What equation must x_0,x_1,x_2 obey so that the tangent line and secant lines are parallel

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: algebra

Hi kilo123;

Equation y= -(1/x_0+1)^2)x+y_0

Are you sure that is the tangent line at x0?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Kilo123

Member

Registered: 2010-10-04

Posts: 2

Re: algebra

not necessarily, but how many other ways can you represent it? y=1/(x+1)
dy/dx= -1/(x+1)^2

Then formula y-y_0=m(x-x_o)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: algebra

Hi;

Not following you but that is not the tangent line at point (x0,y0) of f(x). Shouldn't you first get the right tangent line.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.