（1）2log5*10+log5*0.25
=log5*10²+log5*0.25
=log5*(10²×0.25)
=log5*25
=log5*5²
=2
(2)log2(log2*16)
=log2*(log2*2^4)
=log2*4
=log2*2²
=2
(3)lg12.5-lg5/8+lg0.5
=lg(12.5×5/8×0.5)
=lg10
=1
第三题：y=√（x²+3x+2）+log2*3x的定义域是?
根号下大于等于0,真数大于0
所以x²+3x+2=(x+1)(x+2)≥0
x≤-2,x≥-1
3x>0
x>0
所以定义域(0,+∞)