1
x=-1
y=2
2x-9y^2=-2-36=-38
2
a0 |a-(-a)|=2|a|=-2a
3
（-1）-｛(-1/2)+[1/3-（1/4-1/6）]｝
=-1-{-1/2+1/3-1/4+1/6}
=-1-{-1/6+1/6-1/4}
=-1-(-1/4)=-1+1/4=-3/4
4.
（-1又1/2）|-（4又¼）-（-2又1/3）|
=-3/2* |-4-¼+2+1/3|
=-3/2*|-2+1/12|
=-3/2*23/12=-23/8
5
1-2+3-4+5-6+...-100+101
=(1-2)+(3-4)+...+(99-100)+101
=-50+101
=51