() () ()=30,1,3,7,9,11,13,15可以重复使用

1、x/1.32=0.5x=1.32*0.5x=0.662x/3+x/4=7/304x/12+3x/12=7/307x/12=7/30x=12/30x=0.4

先求1+2+.+30=31*15=465再算3+6+9..+30=180本题答案为465-180*2=105

1+2-3+4+5-6+7+8-9+10.+28+29-30=0+1+2-3+4+5-6+7+8-9+10.+28+29-30=(0+1+2+3+4+5-6+7+8+9+10.+28+29+30)-2

教学通jxt123com(x-30):(3/7x+30)=3:2得2（x-30）=3（3/7x+30)2x-60=9/7x+90x=270

1+1/3-7/12+9/20-11/30+13/42=1+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7=1+1/7=8/7

1+1/3-7/12+9/20-11/30+13/42-15/56=1+(1/3)-(1/3)-(1/4)+(1/4)+(1/5)-(1/5)-(1/6)+(1/6)+(1/7)-(1/7)-(1/8

第一个是（1+30％）x=260吧（1+30％）x=260130％x=260x×130％÷130％=260÷130％x=2009分之7-660x=6分之1-660x=3/18-14/18-660x=-

5又13/15,2又3/10,7/10,4/15

288/15

408－12×24（46＋28）×6042×50－1715÷532＋105÷5（108＋47）×52420×（327－238）(4121+2389)÷7671×15-974469×12+1492405

去括号得：3x-3-7x-35=30x+30移项合并得：-34x=68化系数为1得：x=-2

3又4/6=22/67又1/12=85/129又1/30=271/3011又1/42=463/42通分原式=420/420+1540/420+1700/420+3794/420+4630/420=12

-1/9原式=-1/3+7/(3x4)-9/(4x5)+11/(5x6)-13/(6x7)+15/(7x8)-17/(8x9)=-1/3+7/3-7/4-9/4+9/5+11/5-11/6-13/6+

每一项可理解为(2a+1）/a（a+1)=1/a+1/(a+1)原式=1-1-1/2+1/2+1/3-1/3-1/4...-1/9-1/10+1/10+1/11=1/11

2\3乘(x-30)=3\7x+30两边乘以2114(x-30)=9x+63014x-14×30=9x+63014x-9x=630+4205x=1050x=1050÷5x=210

（-1/42)除以（1/6-3/14+2/3-2/7）=-1÷（42×1/6-42×3/14+42×2/3-42×2/7）=-1÷（7-9+28-12）=-1÷14=-1/141又3分之一-7/12+

=4/3+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)=4/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7=5/3-1/7=32/21=1又21分

1又1/3-7/12+9/20-11/30+13/42-15/56=（1+1/3)-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)+(1/6+1/7)-(1/7+1/8)=1-1/8=7/

X^2+X-7=0X1=根29-1X2=-1-根29X^2+X-2=0X1=-2X2=19-6X+X^2+X=9X^2-5X=0X(X-5)=0X1=0X2=5

内项的积等于外项的积.5/3X+150=14/3X-2103X=360X=120再问：那个3X=360是怎么来的？