1,25(a-b)^2-9(a+b)^2
=[5(a-b)+3(a+b)][5(a-b)-3(a+b)]
=(8a-2b)(2a-8b)
=4(4a-b)(a-4b);
2,(a^2+9)^2-4a^4
=(a^2+9-2a)(a^2+9+2a);
3,2^48=2^(6+42)=2^6*2^42=64*2^42,能被64整除;
(应该是题目没抄写完整!)
4.因为m^2=n^2+45,
所以m^2-n^2=45,
所以(m+n)(m-n)=45,45=1*45=3*15=5*9,
因为m+n>m-n,m,n都是正整数,
所以m+n=45,15,9,
m-n=1,3,5,
所以m=23,9,7,
n=22,6,2
所以(m,n)=(23,22),(9,6),(7,2);
5.(1-1/2^2)(-1/3^2)...(1-1/100^2)
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)...(1-1/100)(1+1/100)
=(1/2)*(3/2)*(2/3)*(4/3)*...*(99/100)*(101/100)
=(1/2)*(101/100)
=101/200.
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