填空某次数学测试,有m个同学得a分,有n个同学得b分,则这些同学平均分为_________计算（x-1）2/4x *（2
2个回答

(am+bn)/(m+n)

(x-1)^2/4x *(2x2)/(x-x^2) = (x-1)^2/4x * 4/x(1-x) = (1-x)^2/4x * 4/x(1-x)=(1-x)/x^2

(16-m^2)/(16+8m+m^2)÷(m-4)/(2m+8)*(m^2-4)/(m+2)

=(m+4)(m-4)/(m+4)^2 ÷(m-4)/2(m+4)*(m+2)(m-2)/(m+2)

=(m-4)/(m+4) * 2(m+4)*/(m-4))* (m-2)

=2(m-2)=2m-4

[(x^2-5x+6)/(12-7x+x^2)]^2÷[(x^2+3x+2)/(x^2-2x-8)]^2

=[(x-2)(x-3)/(x-3)(x-4)]^2 ÷ [(x+1)(x+2)/(x+2)(x-4)]^2

=[(x-2)/(x-4)]^2 ÷ [(x+1)/(x-4)]^2

=(x-2)^2/(x-4)^2 * (x-4)^2/(x+1)^2

=(x-2)^2/(x+1)^2

x=-5 原式= (-5-2)^2/(-5+1)^2 =(-7)^2/(-4)^2 = 49/16

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