Let y=y(x) be the solution of the differential equation 2x dx+ (e2y 2x+ x )dy=0, 0<x< 2, y( /4)=0. If y( /6)= , then e8 is equal to .
Answer
9
Solution
Put x=t ( 2x dx=dt): dtdy+t=-e2yt2 (Bernoulli in t)
Divide by t2 and put 1t=u ( dudy=- 1t2 dtdy ): dudy-u=e2y
I.F. =e-y ue-y= eydy=ey+C
x= 4: u= 4=1, y=0 1=1+C C=0
x=e2y
x= 6: e2 = 3 e8 = ( 3 )4=9
Answer: 9