数学 难

你放大一下，传的很辛苦啊！

1)
=√(8+9-12√2)
=√[(2√2)^2-2×3×2√2+3^2)
=√(3-2√2)^2
=3-2√2.

2)
=√[3+2√(17+12√2)]
=√[3+2√(3+2√2)^2]
=√[3+2×(3+2√2)]
=√[9+4√2]
=√[1+2×2√2+8]
=√[1+2×2√2+(2√2)^2]
=√[1+2√2]^2
=1+2√2

3
[√(25-x^2)-√(15+x^2)]^2=(25-x^2)+(15+x^2)-2√(25-x^2)·√(15+x^2)
=40-2√(25-x^2)·√(15+x^2)
=4^2=16,
则2√(25-x^2)·√(15+x^2)=40-16=24;

∴[√(25-x^2)+