中4一條amths!急!

cos6x = cos(2x+4x) =cos2xcos4x - sin2xsin4x
sin6x = sin(2x+4x) = sin2xcos4x +sin4xcos2x

LHS = cos4x - sin2xsin4x/cos2x + cos4x + sin4xcos2x/sin2x
= 2 cos4x - sin2x(2sin2xcos2x)/cos2x + (2sin2xcos2x)cos2x/sin2x
= 2cos4x - 2sin2xsin2x + 2 cox2xcos2x
= 2cos4x + 2(cos2xcos2x - sin2xsin2x)
= 2cos4x + 2cos4x
= 4cos4x
= RHS

Cos6x÷cos2x + sin6x÷sin2x
=( sin2xcos6x + cos2xsin6x ) ÷ sin2xcos2x
=sin ( 2x+6x ) ÷ ½ sin4x → [sin(A+B) ÷ ½sin2A]
=2sin8x ÷ sin4x
=2( 2sin4xcos4x ) ÷ sin4x → [ sin2A=2sinAcosA ]
=4cos4x
=R.H.S

cos6x\cos2x+sin6x\sin2x=(cos6xsin2x+sin6xcos2x)\cos2xsin2x
=sin(6x+2x)\cos2xsin2x
=sin8x\cos2xsin2x
=2sin4xcos4x\cos2xsin2x
=4sin2xcos2xcos4x\cos2xsin2x
=4cos4x