若三點A(-2,-2)B(0,m)C(n,0)(mn不等於0)共線, 則1/m+1/n為多少?

若三點A(-2,-2)B(0,m)C(n,0)(mn不等於0)共線, 則1/m+1/n為多少?

1/m+1/n=(m+n)/mn
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AB=(2,m+2)BC=(n,-m)AC=(n+2,2),又三點A(-2,-2)B(0,m)C(n,0)(mn不等於0)共線,
則(m+2)(n+2)=4 -2m=n(n+2)原式=-1/2