So 2 < c < 2 √ 2
Because the third side is greater than the difference between the two sides is less than the sum of the two sides.
0 < x: 2a+ 1, which means a >；; 2
a^2+(2a- 1)^2>； (2a+ 1)^2
Get a> eight
3. The four roots of the equations X 2-X+A = 0 and X 2-X+B = 0 (A is not equal to B) are
x 1 x2 x3 x4
x 1+x2= 1
x3+x4= 1
Four roots form a arithmetic progression, and the first term is 1/4.
Suppose x 1= 1/4.
The arrangement of the four roots is as follows
x 1 x3 x4 x2
x2=3/4
x3=5/ 12
x4=7/ 12
a=x 1*x2=3/ 16
b=x3*x4=
A+b= just solve it yourself.
4. Consider the monotonicity of the sequence: when n
5.A 1 * A2 * A3 = 9, and A 1 * A2 = 4, so a3=9/4.
A 1A2A3A4A5 = 25, A 1A3A4 = 16, so a5=25/ 16.
So a3+a5 = 6116.
6.an=sn-s(n- 1)=3^n- 1-(3^(n- 1)- 1)=3^n-3^(n- 1)