12(x²+7)²-8(x²+7)(2x-1)-15(2x-1)²
(x²+7)=a
(2x-1)=b
12a²-8ab-15b²=12a²-18ab+10ab-15b²=6a(2a-3b)+5b(2a-3b)=(2a-3b)(6a+5b)
[ 2(x²+7)-3(2x-1) ] [ 6(x²+7)+5(2x-1) ]=
( 2x²+14-6x+3 ) ( 6x²+42+10x-5) )=
(2x²-6x+17)(6x²+10x+37)=
2x²×6x² - 6x × 6x² +17×6x² + 2x²×10x - 6x ×10x+17×10x+2x²×37-6x ×37+17 × 37=
12x⁴ -36x³+102x²+20x³-60x²+170x+74x²-222x+629=
12x⁴ -36x³+20x³+102x²-60x²+74x²+170x-222x+629=
=12x⁴-16x³+116x²-52x+629