Solve the equation (1 Viewer)

[Norma.Jean]

3^2x+2.3^x-15=0

...oh deary me :\

 

[tommykins]

回复: Solve the equation

It's a quadratic.

Let m = 3^x.

 

[Norma.Jean]

oh eff, you are absolutely right i always forget how the . is times :\\\\\\!

 

[Js^-1]

Re: 回复: Solve the equation

Yeh, the answer ends up being x = 1

Haha I made that mistake in year 10 exams. I used logs to solve some some nasty as thing with decimals and it turned out that it was meant to be a dot product...In my defence they were very shoddy dot products...

 

[ratcher0071]

3^2x+2.3^x-15=0

...oh deary me :\

let m=3^x

m² + 2m -15 = 0
(m+5)(m-3)=0
m=-5 or m=3

sub m=3^x into m=3

3^x=3
x=1

 

[Forbidden.]

The other solution isn't called no solution, the 2-unit course covered up complex numbers and therefore the imaginary solution is:
[ln(5) + π i] / ln(3)

Rock On

 

[Norma.Jean]

I was like (looking for updated new posts) ooo Solve The Equation...thinking "oh yes i can contibute back for all the times i asked a million questions"



....and it was my thread :\

 

[ratcher0071]

I was like (looking for updated new posts) ooo Solve The Equation...thinking "oh yes i can contibute back for all the times i asked a million questions"



....and it was my thread :\

lol :rofl:

 

[Js^-1]

Yeh, there is no 'real' solution for 3^x < or = 0

 

[ratcher0071]

Yeh, there is no 'real' solution for 3<SUP>x</SUP> < or = 0

True, if you look at the graph of 3^x you see it is an exponential, cutting the y axis at 1