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D in (-oo:+oo)
(1/8)*D-(3*(D-7)) = (41/8)*D-3 // - (41/8)*D-3
(1/8)*D-(3*(D-7))-((41/8)*D)+3 = 0
(1/8)*D-3*(D-7)+(-41/8)*D+3 = 0
D/8-3*(D-7)+(-41*D)/8+3 = 0
(-3*8*(D-7))/8+D/8+(-41*D)/8+(3*8)/8 = 0
D-3*8*(D-7)-41*D+3*8 = 0
24-23*D-41*D+168 = 0
24-64*D+168 = 0
192-64*D = 0
(192-64*D)/8 = 0
(192-64*D)/8 = 0 // * 8
192-64*D = 0
192-64*D = 0 // - 192
-64*D = -192 // : -64
D = -192/(-64)
D = 3
D = 3
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