(1)1/(x+1)-x+1 (2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)
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(1)1/(x+1)-x+1 (2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1) (3)20^2-20*38+19^2
(1)1/(x+1)-x+1 (2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)
(3)20^2-20*38+19^2
(4)899^2-101^2 (5)1/2* 3.7^2-3.7*2.7+1/2* 2.7^2
(1)1/(x+1)-x+1 (2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)
(3)20^2-20*38+19^2
(4)899^2-101^2 (5)1/2* 3.7^2-3.7*2.7+1/2* 2.7^2
![(1)1/(x+1)-x+1 (2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)](/uploads/image/z/9234504-0-4.jpg?t=%EF%BC%881%EF%BC%891%2F%EF%BC%88x%2B1%EF%BC%89-x%2B1+%282%292%2F%28a%2B1%29-%28a-2%29%2F%28a%5E2-1%29%C3%B7%28a%5E2-2a%29%2F%28a%5E2-2a%2B1%29)
(1)1/(x+1)-x+1
=1/(x+1)-(x-1)
=1/(x+1)-(x-1)(x+1)/(x+1)
=1/(x+1)-(x^2-1)/(x+1)
=-x^2/(x+1)
(2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)
=2/(a+1)-(a-2)/[(a+1)(a-1)]×(a-1)^2/[a(a-2)]
=2/(a+1)-(a-1)/[a(a+1)]
=[2a-(a-1)]/[a(a+1)]
=(a+1)/a(a+1)
=1/a
(3)20^2-20*38+19^2
=20^2-2×20×19+19^2
=(20-19)^2
=1
(4)899^2-101^2
=(899+101)*(899-101)
=1000*798
=798000
(5)1/2* 3.7^2-3.7*2.7+1/2* 2.7^2
=1/2*( 3.7^2-2*3.7*2.7+ 2.7^2)
=1/2*(3.7-2.7)^2
=1/2
再问: �����ⷽ�̣�x^2-12x=0 x^2-1/4=0
再答: x^2-12x=0 x(x-12)=0 x1=0,x2=12 x^2-1/4=0 x^2=1/4 x1=1/2,x2=-1/2
=1/(x+1)-(x-1)
=1/(x+1)-(x-1)(x+1)/(x+1)
=1/(x+1)-(x^2-1)/(x+1)
=-x^2/(x+1)
(2)2/(a+1)-(a-2)/(a^2-1)÷(a^2-2a)/(a^2-2a+1)
=2/(a+1)-(a-2)/[(a+1)(a-1)]×(a-1)^2/[a(a-2)]
=2/(a+1)-(a-1)/[a(a+1)]
=[2a-(a-1)]/[a(a+1)]
=(a+1)/a(a+1)
=1/a
(3)20^2-20*38+19^2
=20^2-2×20×19+19^2
=(20-19)^2
=1
(4)899^2-101^2
=(899+101)*(899-101)
=1000*798
=798000
(5)1/2* 3.7^2-3.7*2.7+1/2* 2.7^2
=1/2*( 3.7^2-2*3.7*2.7+ 2.7^2)
=1/2*(3.7-2.7)^2
=1/2
再问: �����ⷽ�̣�x^2-12x=0 x^2-1/4=0
再答: x^2-12x=0 x(x-12)=0 x1=0,x2=12 x^2-1/4=0 x^2=1/4 x1=1/2,x2=-1/2
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