Question

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Answer 1

S△abc=1/2AC×BC=1/2×3×4=6
AC×BC=CD×AB
CD=AC×BC/AB=3×4/5=12/5

Answer 2

(2)AC垂直于AB，CD垂直于A
AB的高为CD
AC=CD
CD=AC=3

Answer 3

因为AC²+BC²=AB²，所以三角形ABC为Rt△

追答

所以∠ACB=90°

Answer 4

（3x4）除2=6

Answer 5