Let y=y(x) be the solution of the differential equation (x+1)y′−y=e3x(x+1)2, with y(0)=13. Then, the point x=−43 for the curve y=y(x) is:
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Solution
(x+1)dydx−y=e3x(x+1)2 dydx−yx+1=e3x(x+1) I.F=e−∫1x+1dx=e−log(x+1)=1x+1 ∴y(1x+1)=∫e3x(x+1)x+1dx yx+1=∫e3xdx yx+1=e3x3+C ∵y(0)=13 13=13+C ∴C=0
So: y=e3x3(x+1) y′=e3x(x+1)+e3x3=e3x(x+43) y′′=3e3x(x+43)+e3x=e3x(3x+5) y′=0 at x=−43&y′′=e−4(1)>0 at x=−43 ⇒x=−43 is point of local minima.