对一楼进行一下补充,加上括号就明显很多!
3.
a-b=[a^(1/3)]^3-[b^(1/3)]^3=[a^(1/3)-b^(1/3)][a^(2/3)+(ab)^(1/3)+b^(2/3)] 【立方公式前面为-后面为+】
(a-b)÷（a1/3次方-b1/3次方）=a^(2/3)+(ab)^(1/3)+b^(2/3)
7
(3)(lg5)^2+lg2lg(2*5^2)=(lg5)^2+lg2(lg2+2lg5)=(lg5)^2+2lg2lg5+(lg2)^2
=(lg2+lg5)^2=(lg10)^2=1
(4)(lg^5-lg^2)/(lg25-lg4)=(lg^5-lg^2)/(2lg5-2lg2)=1/2(lg5+lg2)=1/2*lg10=1/2