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例1 (第八届“五羊杯”初中数学竞赛试题)若a-2b+3c=7,4a+3b-2c=3,则5a+12b-13c=( ). A.30 B.-30 C.15 D.-15 解:设5a+12b-13c=l(a-2b+3c)+m(4a+3b-2c).
Example 1 (what is the question of the eighth “Wuyang Cup” junior high school mathematics competition) If a-2b+3c=7,4a+3b-2c=3, then 5a+12b-13c=( ). A.30 B.-30 C.15 D.-15 Solution: Let 5a+12b-13c=l(a-2b+3c)+m(4a+3b-2c).