Maths Problem

MathsNerd31

Can anyone solve this for me? It's too late on a Friday. I'm trying to get it using logs but keep backing myself into a corner.

(0.5)^x=-3x-1

ZorbaTehZ

Is this from homework? Are you allowed to express the answer in terms of other functions? Because I think this is a transcendental equation so it does not have a closed-form solution...

MathsNerd31

Not for homework. A teacher friend of mine is looking for a solution and foolishly thought I'd be able to help. I think it was thrown at him by a student. A solution to it is x=-1 but not sure if there are others.

SHANAbert

x^2 + 6x + 2 = 0

x = -1 is not a solution.

Work out the -b formula

Pembily

Mod note: no solutions please, just advice.

greedygoblin

MathsNerd31 wrote: »

Not for homework. A teacher friend of mine is looking for a solution and foolishly thought I'd be able to help. I think it was thrown at him by a student. A solution to it is x=-1 but not sure if there are others.

Let [latex] f(x) = 0.5^x [/latex]and plot.
Let [latex] f(x) = -3x-1 [/latex] and plot.

The intersection of the two curves should give you your root(s)...

ZorbaTehZ

MathsNerd31 wrote: »

Not for homework. A teacher friend of mine is looking for a solution and foolishly thought I'd be able to help. I think it was thrown at him by a student. A solution to it is x=-1 but not sure if there are others.

There are exactly 2 which should be fairly easy to see if you plot both sides - the other one is only a little smaller than -1.

SHANAbert wrote: »

x^2 + 6x + 2 = 0

x = -1 is not a solution.

Work out the -b formula

Er x=-1 is a solution, but neither root of your quadratic is a solution to the OPs equation.

Ciaran

SHANAbert wrote: »

x^2 + 6x + 2 = 0

x = -1 is not a solution.

Work out the -b formula

It's 0.5 to the power of x, not 0.5 by x squared.

Graphing it is the quickest way to get a numerical solution. If the teacher wants the student to work it out by hand, they can use the Newton-Raphson method.

mathsnerd33

SHANAbert wrote: »

x^2 + 6x + 2 = 0

x = -1 is not a solution.

Work out the -b formula

Thanks but that's not the equation. Thanks everyone else too. I've got it now.