Download - Double Angle Formulas
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Double Angle Formulas
sin 2x = sin ( x + x ) = sinx cosx + cosx
sinx = 2 sinx cosx
cos 2x = cos2x – sin2x
= ( 1 – sin2x ) – sin2x= 1 – 2 sin2x
= cos2x – ( 1 – cos2x = 2cos2x - 1
Verify the Identity:
sec 2x = cos²x + sin²x cos²x - sin²x
1 = 1
cos 2x cos 2x
cos A - sin A = cos 2A cosA + sin A
Cross-multiply:(cosA-sinA)
(cosA+sinA)=cos2Acos²A-sin²A = cos 2A
cos 2A = cos 2A
tan 1/2 A = sin A 1 + cos A
1 - cos A = sin A sin A 1 + cos A
cross-multiply:1 - cos²A = sin² A sin² A = sin² A