# Thread: trigo and log equation

1. ## trigo and log equation

Solve in R :

2. Originally Posted by dhiab
Solve in R :
I will try

let $\displaystyle t=\pi (ln(x^2))$

[tex]sint + cost = 1 [tex]

$\displaystyle 2sin(t)cos(t) + 1 - 2sin^2(t) = 1$

$\displaystyle 2sin(t)(cos(t) - sin(t)) = 0$

$\displaystyle sint=0........ln(x^2)=0.....x=\pm 1$

$\displaystyle sint=cost....t=\frac{\pi}{4} + 2\pi n .....$

$\displaystyle \pi ln(x^2)=\pi ( \frac{1}{4} + 2n )$

$\displaystyle ln(x^2)= \frac{1}{4} + 2n$

$\displaystyle x^2 = e^{.75 + 2n }$

$\displaystyle x= e^{.375 + n }$

3. Originally Posted by Amer
I will try

let $\displaystyle t=\pi (ln(x^2))$

[tex]sint + cost = 1 [tex]

$\displaystyle 2sin(t)cos(t) + 1 - 2sin^2(t) = 1$

$\displaystyle 2sin(t)(cos(t) - sin(t)) = 0$

$\displaystyle sint=0........ln(x^2)=0.....x=\pm 1$

$\displaystyle sint=cost....t=\frac{\pi}{4} + 2\pi n .....$

$\displaystyle \pi ln(x^2)=\pi ( \frac{1}{4} + 2n )$

$\displaystyle ln(x^2)= \frac{1}{4} + 2n$

$\displaystyle x^2 = e^{.75 + 2n }$

$\displaystyle x= e^{.375 + n }$
Hello Amer
here is expression just : sint = 2sin(t/2)cos(t/2) and :
cost = 1-2sin2 (t/2)
TANK YOU

4. Originally Posted by dhiab
Solve in R :
Divide by $\displaystyle \sqrt{2}$ on both sides

$\displaystyle \sin \frac{\pi}{4} \sin \pi ln(x^2)+\cos \frac{\pi}{4} \cos \pi ln(x^2)=\frac{1}{\sqrt{2}}$

$\displaystyle \cos(\frac{\pi}{4}+\pi ln(x^2))=\cos\frac{\pi}{4}$

$\displaystyle \frac{\pi}{4}+\pi ln(x^2)=2n\pi \pm \frac{\pi}{4}$

$\displaystyle ln(x^2)=2n$;$\displaystyle x^2=e^{2n}$;$\displaystyle x=e^{n}$

$\displaystyle ln(x^2)=\frac{1}{2}-2n$;$\displaystyle x^2=e^{\frac{1}{2}-2n}$;$\displaystyle x=e^{\frac{1}{4}-n}$

'n' being any integer

5. Originally Posted by pankaj
Divide by $\displaystyle \sqrt{2}$ on both sides

$\displaystyle \sin \frac{\pi}{4} \sin \pi ln(x^2)+\cos \frac{\pi}{4} \cos \pi ln(x^2)=\frac{1}{\sqrt{2}}$

$\displaystyle \cos(\frac{\pi}{4}+\pi ln(x^2))=\cos\frac{\pi}{4}$

$\displaystyle \frac{\pi}{4}+\pi ln(x^2)=2n\pi \pm \frac{\pi}{4}$

$\displaystyle ln(x^2)=-2n$;$\displaystyle x^2=e^{-2n}$;$\displaystyle x=e^{-n}$

$\displaystyle ln(x^2)=\frac{1}{2}-2n$;$\displaystyle x^2=e^{\frac{1}{2}-2n}$;$\displaystyle x=e^{\frac{1}{4}-n}$

'n' being any integer
Hello : i' cannot understing this resolution :
Thank you

6. I made a mistake.I have edited my post.