回復 1# g112 的帖子
第2題
\(A\left( 2,-7 \right),B\left( 8,2 \right)\)對\(y=-x\)鏡射後為\(A'\left( 7,-2 \right),B'\left( -2,-8 \right)\)
\(A'\left( 7,-2 \right),B'\left( -2,-8 \right)\)沿x軸推移y坐標的2倍後是\(A''\left( 3,-2 \right),B''\left( -18,-8 \right)\)
所求為\(\overline{A''B''}=\sqrt{{{21}^{2}}+{{6}^{2}}}=3\sqrt{53}\)