9çm次æ¹Ã3çn次æ¹
=3^2mÃ3^n
=3^(2m+n)
=3^2
=9
è¥2ç2x+3次æ¹-2ç2x+1次æ¹=48ï¼æ±xçå¼ã
2^(2x+3)-2^(2x+1)=48
2^(2x+1)(2^2-1)=48
2^(2x+1)=16=2^4
2x+1=4
x=3/2
è¥xç2n次æ¹=2ï¼æ±ï¼-3xç3n次æ¹ï¼²-4ï¼-x²ï¼ç2n次æ¹çå¼
ï¼-3xç3n次æ¹ï¼²-4ï¼-x²ï¼ç2n次æ¹
=9x^(6n)-4*(x^(4n))
=9*(x^2n)^3-4[x^(2n)]^2
=9*2^3-4*2^2
=72-16
=56
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