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June 9th, 2019, 03:50 AM  #1 
Senior Member Joined: Dec 2015 From: somewhere Posts: 634 Thanks: 91 
Equation : $\displaystyle y’’=y$. Add both sides +y’ then substitution as $\displaystyle y’+y=t$. $\displaystyle t’=t$. Is this way correct? Last edited by skipjack; June 9th, 2019 at 10:18 AM. 
June 9th, 2019, 05:25 AM  #2 
Senior Member Joined: Sep 2015 From: USA Posts: 2,549 Thanks: 1399 
The usual way is to form the characteristic equation. $y''y=0$ $s^2  1= 0$ $s = \pm 1$ $y = c_1 e^t + c_2 e^{t}$ 
June 9th, 2019, 08:08 AM  #3 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,838 Thanks: 653 Math Focus: Yet to find out. 
Also the chant "what when differentiated twice equals itself!"

June 9th, 2019, 10:02 AM  #4 
Senior Member Joined: Sep 2015 From: USA Posts: 2,549 Thanks: 1399  
June 9th, 2019, 10:24 AM  #5 
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June 9th, 2019, 02:40 PM  #6 
Math Team Joined: May 2013 From: The Astral plane Posts: 2,266 Thanks: 933 Math Focus: Wibbly wobbly timeywimey stuff.  

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