Verified answer

aki estan los 4 resueltos ojala te sirva

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http://i34.tinypic.com/67ts76.jpg

a) secA - cosA = senA.tanA

= 1/cosA - cosA

= (1 - cos^2A)/cosA

= sen^2A/cosA

= (senA)(senA/cosA)

= senA.tanA

b) sec^2A + csc^2A = sec^2Acsc^2A

= 1/(cos^2A) + 1/(sen^2A)

= (sen^2A + cos^2A)/cos^2A.sen^2A

= 1/cos^2A.sen^2A

= (1/cos^2A)(1/sen^2A)

= sec^2A.csc^2A

c) cosA + senA.tanA = secA

= cosA +senA(senA/cosA)

= (cos^2A + sen^2A)/cosA

= 1/cosA

= secA

d) cscA - cosA.cotA = senA

= 1/senA - cosA(cosA/senA)

= 1/senA - cos^2A/senA

= (1 - cos^2A)/senA

= sen^2A/senA

= senA

Es todo, ojalá lo entiendas, adiós.