$(7x+3b)^3-(5x+3b)^3-6x(7x+3b)(5x+3b)$
$=(7x+3b)^3-(5x+3b)^3-3\cdot(7x+3b)(5x+3b)\cdot2x$
ধরি,
$(7x+3b)=p$ এবং $(5x+3b)=q$
এখন,
$p-q$
$=(7x+3b)-(5x+3b)$
$=7x+3b-5x-3b$
$=2x$
সুতরাং পদত্ত রাশি দাঁড়ায়,
$p^3-p^3-3\cdot pq\cdot(p-q)$
$=p^3-p^3-3pq(p-q)$
$=(p-q)^3$
$=(2x)^3$
$=8x^3$ [Answer]
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