求解这一步的详细过程
2018-07-03
展开全部
|x1-x2|=√(x12+x22-2x1x2) =√(x12+x22+2x1x2-4x1x2) =√[(x12+x22+2x1x2)-4x1x2] =√[(x1+x2)2-4x1x2] =√[(16k/(1+4k2)2-4·12/(1+4k2)] =√(64k2-48) /(1+4k2) =4√(4k2-3) /(1+4k2) |PQ|=√(k2+1)|x1-x2|=√(k2+1)·4√(4k2-3) /(1+4k2)=4√(k2+1)√(4k2-3) /(1+4k2)
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