8/27a^3-1/64b^3 = (2/3a-1/2b) (4/9a^2+1/12ab+1/4b^2)

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(1) (8/27) a^3 - (1/64) b^3 = ((2/3) a-1/2b) ((4/9) a^2 + (1/12) ab + (1/4) b^2)

(8/27) ·a^3 - (1/64) ·b^3 = ((2/3) a) ^3 - ((1/4) b) ^3=[ (2/3) ·a - (1/4) b]·[ ((2/3) a) ^2 + (2/3) a· (1/4) b + ((1/4) b) ^2] = ((2/3) a-1/2b) ((4/9) a^2 + (1/12) ab + (1/16) b^2) (2)

(1/4) b^2) - последнее слагаемое (1) не совпадает с последним слагаемым (2), скорее не верно записано ...