✔ 最佳答案
Sol
(1)
6+9=10+5=13+2
x=√6+3=√6+√9
x^2=15+2√54
y=√10+√5
y^2=15+2√100
z=√13+√2
z^2=15+2√52
So
y^2>x^2>z^2
x>0,y>0,z>0
y>x>z
(2)
10-5=12-7=8-3
a=√10-√5
=(√10-√5)(√10+√5)/(√10+√5)
=5/(√10+√5)
b=√12-√7
=(√12-√7)(√12+√7)/(√12+√7)
=5/(√12+√7)
c=√8-√3
=(√8-√3)(√8+√3)/(√8+√3)
=5/(√8+√3)
5/(√8+√3)>5/(√10+√5)>5/(√12+√7)
c>a>b
(4)
1+27x^3
=1^3+(3x)^3
=(1+3x)*(1-3x+9x^2)
(5)
x^4-256
(x^2)^2-(16)^2
=(x^2-16)(x^2+16)
=(x-4)(x+4)(x^2+16)
(6)
(a+b)^4-(a-b)^4
=[(a+b)^2-(a-b)^2]*[(a+b)^2+(a-b)^2]
=[(a+b)-(a-b)]*[(a+b)+(a-b)]*(2a^2+2b^2)
=2b*2a*2(a^2+b^2)
=8ab(a^2+b^2)