1.Cho a/b=c/d . Chứng minh rằng
a)a-c/c=b-d/a
b)a/b=a+c/b+d
c)a+b/a-b=c+d=c-d
d)7a22+3ab/11a2-8b2
e)a/b=3a+2c/3b+2d
f)a/a+b=c/c+d
g)2a+5b/3a-4b=2c+5d/3c-4d
h)a2+c2/b2+d2=a.c/b.d
2.
a)Cho a2/b.c . Chứng minh a+b/a-b=c+a/c-a
b)Cho b2 =a.c . Chứng minh a2+b2/b2+c2=a/c
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