Prove that: (i) cos(A+B+C)+cos(−A+B+C)+cos(A−B+C)+cos(A+B−C)sincos(A+B+C)+sincos(−A+B+C)+sincos(A−B+C)−sin(cos(A+B−C)) (ii) sin(B−C)cos(A−D)+sin(C−A)cos(B−D)+sin(A−B)cos(C−D)=0