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Exercicios resolvidos James Stewart vol. 2 7ª ed - ingles

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212 D CHAPTER 14 PARTIAL DERIVATIVES<br />

49. Let u =X + at, v =X - at. Then z = f(u) + g(v), so azjau ~ f'(u) and azjav ~ g 1 (v) .<br />

az f}z aU az av 1 1<br />

Thus at = au at + av at = af (u)- ag (v) and<br />

8 2 z = 2._ [/1( ) - I( )] = (df'(u) 8u - dg 1 (v ) au ) = 2/"( ) 2 " ( )<br />

[)t2 a at u g v a du 8t dv 8t a u + a g v .<br />

S .. , 8z fl( ) I( ) 8 2 z !"( ) "( )' 8 2 z 2 8 2 z<br />

tmt arly .,-- = u + g v and

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