已知m=6^7,n=7^6,
42^42 =[(6×7)^(6×7)]×[(6×7)^(6×7)]
=6^(6×7)7^(6×7)6^(6×7)7^(6×7)
=[(6^7)^6][(7^6)^7][(6^7)^6][(7^6)^7]
=(m^6×n^7)(m^6×n^7)
=m^12×n^14
2.已知a-b=n,
(3a-3b)^3 =27(a-b)^3=27n^3
3.要使x(x^2+a)+3x-2b=x^3+5x+4
则x^3+ax+3x-2b=x^3+5x+4
x^3+(a+3)x-2b=x^3+5x+4
要使x^3+(a+3)x-2b=x^3+5x+4恒成立,
则a+3=5,-2b=4
即a=2,b=-2