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    				| 1. | 
                                    If y = etan^-1 x, show that (1 + x2) y” + (2x – 1) y’ = 0 | 
                            
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Answer»  y = etan^-1 x y = etan^-1 x 1/(1 + x2) ⇒ y’ = y/(1 + x2) ⇒ y'(1 + x2) = y Differentiating w.r.to x y’ (2x) + (1 + x2) (y”) = y’ (i.e.) (1 + x2) y” + y’ (2x) – y’ = 0 (i.e.) (1 + x2) y” + (2x – 1) y’ = 0  | 
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