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聯立方程(20點)
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23,24題 請先另存圖片 圖片參考：http://imgcld.yimg.com/8/n/HA00230702/o/701002190102013873402360.jpg 更新: 23. (4)*4 +(3), (-48+1)b + (40+7)=0 呢度唔明
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23.) ax+by+7=0 ---------(1) 3bx+ay+10=0 --------(2) Given that x =-4, y=1, From (1), -4a+b+7=0 --------(3) From (2), -12b+a+10=0 ---------(4) (4)*4 +(3), (-48+1)b + (40+7)=0 -47b=-47 b=1 Sub b=1 into(3), -4a+1+7=0 -4a=-8 a=2 24a.) 3a-2b=18---------(1) a+b=21--------(2) (1)+(2)*2, (3+2)a = 18+21*2 5a=60 a=12 Sub a=12 into(2), 12+b=21 b=9 b.) 3/x - 2/y = 18 ---------(3) 1/x+1/y = 21 ---------(4) Let a be 1/x, and b be 1/y, Hence, from (3), 3a-2b=18 from(4), a+b=21 a=12, b=9 1/x = 12 x = 1/12 1/y=9 y=1/9 2010-02-19 17:21:44 補充： (4)*4 +(3), (-48+1)b + (40+7)=0 (4)代表已標的第4條equation: From (2), -12b+a+10=0 ---------(4) (3)代表已標的第3條equation: -4a+b+7=0 --------(3) (4)*4 : -12*4b+4a+40=0 (4)*4+(3) : -12*4b+4a+40+(-4a+b+7)=0+0 -48b+4a+40-4a+b+7=0 (-48+1)b+(4-4)a+(40+7)=0 (-48+1)b + (40+7)=0
聯立方程(20點)
發問:
23,24題 請先另存圖片 圖片參考：http://imgcld.yimg.com/8/n/HA00230702/o/701002190102013873402360.jpg 更新: 23. (4)*4 +(3), (-48+1)b + (40+7)=0 呢度唔明
最佳解答:
23.) ax+by+7=0 ---------(1) 3bx+ay+10=0 --------(2) Given that x =-4, y=1, From (1), -4a+b+7=0 --------(3) From (2), -12b+a+10=0 ---------(4) (4)*4 +(3), (-48+1)b + (40+7)=0 -47b=-47 b=1 Sub b=1 into(3), -4a+1+7=0 -4a=-8 a=2 24a.) 3a-2b=18---------(1) a+b=21--------(2) (1)+(2)*2, (3+2)a = 18+21*2 5a=60 a=12 Sub a=12 into(2), 12+b=21 b=9 b.) 3/x - 2/y = 18 ---------(3) 1/x+1/y = 21 ---------(4) Let a be 1/x, and b be 1/y, Hence, from (3), 3a-2b=18 from(4), a+b=21 a=12, b=9 1/x = 12 x = 1/12 1/y=9 y=1/9 2010-02-19 17:21:44 補充： (4)*4 +(3), (-48+1)b + (40+7)=0 (4)代表已標的第4條equation: From (2), -12b+a+10=0 ---------(4) (3)代表已標的第3條equation: -4a+b+7=0 --------(3) (4)*4 : -12*4b+4a+40=0 (4)*4+(3) : -12*4b+4a+40+(-4a+b+7)=0+0 -48b+4a+40-4a+b+7=0 (-48+1)b+(4-4)a+(40+7)=0 (-48+1)b + (40+7)=0
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