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a) x ∈ {-2;-1;;0;1;2;3}
b) x ∈ {10;11;12}
c) x ∈ {0;1;2;3;4;5}
d) x ∈ {-1;0;1;2}
S = 1 - 17/6 + 31/12 - 49/20 + 71/30 - 97/42 + 127/56 - 161/72 + 199/90
S = (1 - 17/6) + (31/12 - 49/20) + (71/30 - 97/42) + (127/56 - 161/72) + 199/90
S = -11/6+2/15+2/35+2/63+199/90
S = 3/5
\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)
\(=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)
\(=9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)
\(=9-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)
\(=9-\left(1-\frac{1}{10}\right)\)
\(=9-\frac{9}{10}=\frac{81}{10}\)
a: =-48+27+56-48-27-36
=-96+20
=-76
b: =23-57+57-33=-10
c: =-98+12-159-12-41
=-98-200
=-298
789. 2- 56+ (-95)+111+261+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
= 1578- 56+ (-95)+111+261+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1522+ (-95)+111+261+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1427+111+261+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1538+261+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1799+498-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2297-215+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2082+49+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2131+1236-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=3367-4591-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=-1224-56+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=-1280+4189+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2909+48+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2957+52-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=3009-1000-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=2009-500+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1509+230+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=1739+32500-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=34239-5600+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=28639+2641+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=31280+853+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=32133+195-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=32328-564+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=31764+235+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=31999+4187+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=36186+9023177-5000000+562+159-90+459-420+562+235+489+71+12
=9059363-5000000+562+159-90+459-420+562+235+489+71+12
=4059363+562+159-90+459-420+562+235+489+71+12
=4059925+159-90+459-420+562+235+489+71+12
=4060084-90+459-420+562+235+489+71+12
=4059994+459-420+562+235+489+71+12
=4060453-420+562+235+489+71+12
=4060033+562+235+489+71+12
=4060595+235+489+71+12
=4060830+489+71+12
=4061319+71+12=4061402
ủa:q. rảnh v:))