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方程式題一問!!請高手指教!

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方程式問題一問.. 我今年升中一..做暑期作業既時候.... 發現有d題目呀sir係學校都冇教過.. 麻煩各位幫幫我... 順便教埋計既方法! 1.(4s-s)+4=28 2.4t-6=4-t 3.4(u+5)+2(u-5)=70 4.2w+w/4=45 5.y+3/4y+70=280

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1.(4s-s)+4=28 =>3s+4=28 =>3s+4-4=28-4 =>3s=24 =>3s/3=24/3 =>s=8 **要兩面一起約** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif eg.3s+4=28 3s+4-4=28-4 3s=28-4 3s=24 3s/3=24/3 s=24/3 s=8 4t-6=4-t =>4t-6+t=4-t+t =>5t-6=4 =>5t-6+6=4+6 =>5t=10 =>5t/5=10/5 =>t=10/5 =>t=2 **要兩面一起約** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif Is same!!(In1. | 2.) 3.4(u+5)+2(u-5)=70 =>4u+4*5+2(u-5)=70 =>4u+20+2u-2*5=70 =>6u+20-10=70 =>6u+10=70 =>6u+10-10=70-10 =>6u=60 =>6u/6=60/6 =>u=10 **拆式** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif eg. a(b+c)+a(b-c) =>ab+ac+ab-ac =>ab+ab =>2ab 4.2w+w/4=45 =>2w*4/4+w/4=45 =>8w/4+w/4=45 =>9w/4=45 =>9w/4*4=45*4 =>9w=180 =>9w/9=180/9 =>w=20 **運用"先乘後除法"組合出"單一數"** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif eg.ab+b/c=d ab*c/c+b/c=d abc/c+b/c=d (abc+b)/c=d **合式** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif (abc+b)/c=d (ac+1)*b/c=d (ac+1)*b/c*c=d*c (ac+1)*b=cd (ac+1)*b/b=cd/b ac+1=cd/b (a+1/c)*c=cd/b (a+1/c)*c/c=cd/b/c a+1/c=d/b 5.y+3/4y+70=280 =>y+3/4y+70-70=280-70 =>y+3/4y=210 =>(1+3/4)y=210 =>1.75y=210 =>1.75y/1.75=210/1.75 =>y=120 **要兩面一起約** 圖片參考：http://l.yimg.com/f/i/tw/ugc/rte/smiley_14.gif Hope I Can Help You

其他解答:

1. (4s-s)+4=28 4s-s=24 3s=24 s=8 2. 4t-6=4-t 4t+t=4+6 5t=10 t=2 3. 4(u+5)+2(u-5)=70 4u+20+2u-10=70 6u=60 u=10 4. 2w+w/4=45 8w+w=180 9w=180 w=20 5. y+3/4y+70=280 y+3/4y=210 4y+3y=840 7y=840 y=120|||||1.(4s-s)+4=28 (4s-s)=28-4 3s=24 s=8 2.4t-6=4-t 4t+t=4+6 5t=10 t=2 3.4(u+5)+2(u-5)=70 4u+20+2u-10=70 6u+10=70 6u=70-10 6u=60 u=10 4.2w+w/4=45 (2w x 4)+(w/4 x 4)=45 x 4 8w+w=180 9w=180 w=20 5.y+3/4y+70=280 (y x4 ) + (3/4y x 4) + 70x4 = 280x4 4y+3y+280=1120 7y=1120-280 7y=840 y=120|||||1. 只要兩邊做相同既野就ok 2. 拆括號按以下規則: a(b + c) = ab + ac, 其中a, b ,c 為任何數 (4s-s)+4=28 (4s-s)+4 - 4= 28 - 4 (4s-s)=24 3s =24 3s/3 = 24/3 s = 8 4t-6=4-t 4t- 6 + 6 =4 - t + 6 4t =4 + 6 -t 4t = 10 - t 4t + t = 10 - t + t 4t + t = 10 5t = 10 5t/5 =10/5 t = 2 4(u+5)+2(u-5)=70 4u + (4)(5)+ 2u +(2)(-5) =70 4u + 20 + 2u -10 =70 6u +10 = 70 6u +10 -10 = 70 - 10 6u = 60 6u/6 =60/6 u =10 2w+w/4=45 ( 2 + 1/4)w = 45 (9/4) w = 45 9w/4= 45 9w/4 x 4 = 45x 4 9w = 180 9w/9 = 180/9 w =20 或者係 (2w+w)/4=45 (2w+w)/4 x 4 =45 x 4 2w+w = 180 3w = 180 3w/3 =180/3 w =60 y+(3/4)y+70=280 y+(3/4)y+70 - 70=280-70 y+(3/4)y=210 (1 + 3/4)y=210 (7/4)y=210 7y/4 =210 7y/4 x 4 = 210 x 4 7y = 840 7y/7 =840/7 y= 120