Question

cos 3A-2 cos 4A
------------------------- ( When A = 15°)
sin 3A + 2 sin 4A​

Answer 1

Answer:

ICSE Class 9

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Sum

Evaluate :

AA

AA

cos3A–2cos4Asin3A+2sin4A , when A = 15°

SOLUTION

(i) Given that A= 15°

AA

AA

cos3A–2cos4Asin3A+2sin4A=cos(3x15°)–2cos(4x15°)sin(3x15°)+2sin(4x15°)

=

cos45°–2cos60°sin45°+2sin60°

=

12–2(12)12+2(32)

=

12–112+3

=

1–21+6

=

Answer 2

Answer:

sin3A+2sin4A

m=____________

cos3A−2cos4A

m= sin45° +2sin60°

cos45°−2cos60°

1

____-1

√2

m= __________

1

_____+3

√2

1-√2

m= _____

1+√6