# Check the answer of a differential equation when I put it in Wolfram Alpha?

GROUPS:
 jorge aldape 1 Vote This: y'''+4y'=sec2x http://www.wolframalpha.com/input/?i=y%27%27%27%2b4y%27=sec2xbrings me this answer:So the circled with red it's incorrect in my opinionProbably the first mistake causes the second.What do you think?
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1 year ago
3 Replies
 Doing this in three steps to get it to fit within the line length limitationIf the supposed solution to the DE is C1 Sin[2x]+C2 Cos[x]^2+C3-x Cos[2x]/4-Log[Cos[x]-Sin[x]]/8+Log[Sin[x]+Cos[x]]/8+Sin[2x]Log[Cos[2x]]/8 then the third derivative seems to bethirdwhich is also -(Sec[2 x] (-2+8 C1+Log[Cos[2 x]]+Cos[4 x] (8 C1+Log[Cos[2 x]])+2 (-2 C2+x) Sin[4 x]))/2 and four times the first derivative seems to befourfirstwhich is also Cos[2 x] (8 C1+Log[Cos[2 x]])+2 (-2 C2+x) Sin[2 x] and the sum of those seems to besumwhich is also Sec[2 x] Can you explain exactly where in these steps you seem to see an error and what the error seems to be?
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1 year ago
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1 year ago
 And my method brings me this answer:
Answer
1 year ago