$a)465+[58+(-465)+(-38)]$

=465+58−465−38$=465+58-465-38$

=(465−465)+(58−38)$=(465-465)+(58-38)$

=0+20$=0+20$

=20$=20$

�)(35−17)+(17+20−35)$b)(35-17)+(17+20-35)$

=35−17+17+20−35$=35-17+17+20-35$

=(35−35)+(−17+17)+20$=(35-35)+(-17+17)+20$

=0+0+20$=0+0+20$

=20$=20$

Nguyễn Quang Hưng: chép!

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