表达式20: StartFraction, left parenthesis, "d" minus 0 , right parenthesis Over left parenthesis, 0 minus "b" , right parenthesis , EndFraction times StartFraction, left parenthesis, "a" minus 0 , right parenthesis Over left parenthesis, 0 minus "c" , right parenthesis , EndFractiond−00−b·a−00−c
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表达式21:
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Can you explain the following?
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When CD and AB are perpendicular, BD and AC must also be perpendicular.
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表达式24:
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You may drag the vertices to change the triangle and test again how might the altitudes meet. Can you make an obtuse triangle?
