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user_id=581700

Perhaps simply rewrite

USIN(N):= BLOCK([YUK:mod(N,20)],

signum(YUK)*(YUK:abs(mod(YUK,10)),

IF YUK=1 THEN (SQRT(5)-1)/4 ELSE

IF YUK=2 THEN (SQRT(5)-1)*SQRT(SQRT(5)+5)/(4*SQRT(2)) ELSE

IF YUK=3 THEN (SQRT(5)+1)/4 ELSE

IF YUK=4 THEN SQRT(SQRT(5)+5)/(2*SQRT(2))))$

UCOS(N):= USIN(5-N)$