R1分之1+R2分之1=?（R1分之1）+（R2分之1）=?（12a²分之5）-（8ab分之3）=?｛（x+1）分之（x

通分
1/R1 + 1/R2 = R2/R1R2 + R1/R1R2 = (R1+R2) / R1R2
5/12a² - 3/8ab = 5b/12a²b - 3a/8a²b = (5b-3a)/8a²b
(x+2)/(x+1) - (x+1)/(x+2) = (x+2)²/(x+1)(x+2) - (x+1)²/(x+1)(x+2)
= [(x+2)²-(x+1)²] / (x+1)(x+2) = (2x+3)/(x+1)(x+2)
(a-1)/(a+1) - 1/a = (a-1)a/a(a+1) - (a+1)/a(a+1) = (a²+1)/a(a+1)
2a/(a²-4) - 1/(a-2) = 2a / (a-2)(a+2) - (a+2)/(a-2)(a+2) = (a-2)/(a-2)(a+2) = 1/(a+2)
(a+2)/(a²-2a) - (a+4)/(a²-4) = (a+2)/a(a-2) - (a+4)/(a-2)(a+2)
= (a+2)²/a(a-2)(a+2) -(a+4)a / a (a-2)(a+2)
= (a+2)² - a(a+4) / a(a-2)(a+2)
= 4/a(a²-4)
= 4/ a3 -4a

R1分之1）+（R2分之1）=1/R1+1/R2=(R1+R2)/R1R2
（12a²分之5）-（8ab分之3）=5/12a²-3/8ab=10b/24a²b-9a/24a²b=(10b-9a)/24a²b
｛（x+1）分之（x+2）｝-｛（x+2）分之（x＋1）｝=
(x+2)/(x+1)-(x+1)/(x+2)=[(x...

1/R1+1/R2
=(R1+R2)/(R1*R2)
5/(12a²)-3/(8ab)
=(10b-39a)/(24a²b)
(x+2)/(x+1)-(x+1)/(x+2)
=1+1/(x+1)-1-1/(x+2)
=1/(x+1)-1/(x+2)
=1/((x+1)(x+2))
(a-1)/(a+1)-1/a

先分母通分，再计算分子。这些题目都不难啊，如果不会通分Hi我。

所有的都是通过通分，将分母化成一样，然后对分子做运算而得出结果
1/R1+1/R2=(R1+R2)/(R1*R2)
5/12a^2-3/8ab=(10b-9a)/(24a^2*b)
(x+2)/(x+1)-(x+1)/(x+2)=(2x+3)/[(x+1)(x+2)]
(a-1)/(a+1)-1/a=(a^2-2a-1)/[a(a+1)]
2a/(a^2-4...