-1*q^3 = -4知q^3 = 4 ,得 q= 根号2；a1 = -根2；a2 = -2;
-1*Q^4 = 4知Q^4 = 4,Q^2 =2;b2 = -1*Q^2 = -2.
答案(a1-a2)/b2=1 + 根2/2;
f(x)=kx+b;f(2)-f(1)= k;f(5)-f(2)=3k; 等差则k=3k,得k=0；
f(3)=b =5,得f(x)=5;故f(1)+f(2)+...+f(10)=50.
ac = b^2,a+b=2m,b+c= 2n,五个未知数,三个方程.
a/m = 2-b/m,c/n=2-b/n;这两式相乘,并利用ac = b^2,
ac/mn = 4+b^2/mn -2b(1/m + 1/n)得4= 2b(1/m + 1/n)即
b(1/m + 1/n)=2;
a/m = 2-b/m,c/n=2-b/n;这两式相加,答案=4-b(1/m+1/n) =4-2=2.