1. The logarithmic function has the property of x >；; 0 and x-8 >; 0; So there is x>8 (1).

Equation deformation: log (subscript 2)[ superscript x*(x-8)] =7.

X*(x-8)= 2 to the 7th power = 128.

The square of x-x * 8- 128 = 0x-x * 8- 16 * 8 = 0 (x- 16) * (x+8) = 0.

The combination formula (1) x >: 8, so the solution of the equation is x= 16.

2. It takes at least X years to be established. Equation: 1*( 1+20%) (marked as x)= 10 (unit: ten thousand vehicles).

The power of the problem is converted into 1.2, which is 10.

The power of 12 of 1.2 is 8.92, and the power of 13 of 1.2 is 10.7, so the answer is at least 13 years.

3.a+b=log (subscript 15) (superscript 7)+log (subscript 15) (superscript 8)=log (subscript 15) (superscript 7*8)=log (subscript/kloc-)

So log (subscript 56) (superscript 15) =1[log (subscript15) (superscript 56)] =1(a+b),

The answer is (a+b) 1: 1/(a+b)