document.write( "Question 532459: Hi tutor, please help me with this question in geometry. I don't understand when to use CPCTC in a proof.. Help? Thankyou \n" ); document.write( "

Algebra.Com's Answer #350847 by KMST(5328) $\"\"$ $\"About$

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CPCTC starts with two Congruent Triangles (CT), and is used when you need to conclude (as the next statement in your proof) that parts (sides or angles) of those triangles are congruent. You need two congruent triangles. Sometimes you are told they are congruent. Sometimes you have just proven that they are congruent.
\n" ); document.write( "If triangles ABC and XYZ are congruent, you can shift, and/or rotate, and/or flip XYZ so as to get X to coincide with A, Y to coincide with B and Z to coincide with C. That means that the Corresponding Parts (CP) of the Congruent Triangles (CT) are Congruent (C).
\n" ); document.write( "You use CPCTC to prove that two segments (a side of one triangle and a side of the other one) are congruent and have the same length. You also use it to prove that two angles (one in each triangle, are congruent and have the same measure. Using CPCTC lets you conclude that since ABC and XYZ are congruent, then side AB is congruent with XY. You could also conclude that angle XYZ is congruent with angle ABC, or that angle BCA is congruent with angle YZX, and so on. \n" ); document.write( "

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