八年级下册数学书第23页第5和第7大题答案
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(1)=x+2y/x+y × xy/x+2y × xy/x+y
=x�0�5y�0�5/x�0�5+2xy+y�0�5
=1/2xy
(2)=b�0�5+a�0�5/a�0�5b�0�5 × a�0�5b�0�5/b�0�5-a�0�5
=b�0�5+a�0�5/b�0�5-a�0�5
(3)=9x^4/16y�0�5 × 2y/3x+x�0�5/2y�0�5 × x/2y�0�5
=3x^3/8y×1+x^3/4y^4
=3x^3+2x^3/8y�0�5
=5x^3/8y�0�5
(4)=(a+b)�0�5/(a-b)�0�5 × 2(a-b)/3(a+b) - a�0�5/(a+b)(a-b) × b/a
=2(a+b)/3(a-b) - ab/(a+b)(a-b)
=2(a+b)�0�5-3ab/3(a+b)(a-b)
=2a�0�5+ab+2b�0�5/3(a+b)(a-b)
=x�0�5y�0�5/x�0�5+2xy+y�0�5
=1/2xy
(2)=b�0�5+a�0�5/a�0�5b�0�5 × a�0�5b�0�5/b�0�5-a�0�5
=b�0�5+a�0�5/b�0�5-a�0�5
(3)=9x^4/16y�0�5 × 2y/3x+x�0�5/2y�0�5 × x/2y�0�5
=3x^3/8y×1+x^3/4y^4
=3x^3+2x^3/8y�0�5
=5x^3/8y�0�5
(4)=(a+b)�0�5/(a-b)�0�5 × 2(a-b)/3(a+b) - a�0�5/(a+b)(a-b) × b/a
=2(a+b)/3(a-b) - ab/(a+b)(a-b)
=2(a+b)�0�5-3ab/3(a+b)(a-b)
=2a�0�5+ab+2b�0�5/3(a+b)(a-b)
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