1) prove cos3A=4cos^3A-3cosA

2) prove 4cos2AsinAcosA =sin4A

6. find real number of x and y such that (2x-j3y)-(1+j5)x=3+j2

ans y=-17/3,x=3

Can anyone provide me the explainations for the above question. i tried hard but i am lost. Help needed.

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- August 11th 2006, 05:56 AMwatsonmathhelp on solving....
1) prove cos3A=4cos^3A-3cosA

2) prove 4cos2AsinAcosA =sin4A

6. find real number of x and y such that (2x-j3y)-(1+j5)x=3+j2

ans y=-17/3,x=3

Can anyone provide me the explainations for the above question. i tried hard but i am lost. Help needed. - August 11th 2006, 06:38 AMgalactus
For #6:

Obviously, x must equal 3

Solve for y. - August 11th 2006, 07:16 AMThePerfectHackerQuote:

Originally Posted by**watsonmath**

Expand,

Double angle identity,

Thus,

- August 11th 2006, 08:57 AMSoroban
Hello, watsonmath!

You need these identities:

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- August 11th 2006, 02:58 PMwatsonmath
BIG thanks guys...