Similar Triangle Proofs | MathHelp.com - Free Educational videos for Students in K-12 | Lumos Learning

Similar Triangle Proofs | MathHelp.com - Free Educational videos for Students in k-12


Similar Triangle Proofs | MathHelp.com - By MathHelp.com



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00:0-1 in this example , we're asked to determine if each
00:03 of the following pairs of triangles are similar In part
00:07 a notice that were only given one pair of congruent
00:11 angles the 60° angles . But remember that the sum
00:20 of the measures of the angles of a triangle is
00:22 180°. . So we can determine that the measure of
00:27 the missing angle of the first triangle is 55° Because
00:35 65 plus 60 plus 55 equals 180 . Now we
00:42 have two pairs of congruent angles , the 55° angles
00:51 And the 60° Angles . Therefore , since two of
00:56 the angles of one triangle are congruent to two of
00:59 the angles of the other triangle , we can say
01:02 that yes , the triangles are similar by the angle
01:06 angle similarity postulate it . Yeah . Yeah . In
01:17 part B since we're given that the lines at the
01:20 top and the bottom of the figure are parallel ,
01:23 we can mark the alternate interior angles at the upper
01:27 left and lower right as congruent because if two parallel
01:34 lines are cut by a transfer cell , then alternate
01:38 interior angles are congruent notice , however , that there
01:44 are no other pairs of angles that can be marked
01:46 as congruent . So we do not know if these
01:49 triangles are similar because we only have one pair of
01:53 congruent angles , so we cannot use the angle angle
01:57 similarity postulate . In this situation , we write that
02:02 the triangle similarity cannot be determined . Yeah . Yeah
02:19 . In part C notice that the small triangle and
02:24 the large triangle both have a right angle . Also
02:29 noticed that these triangles share the angle at the lower
02:33 left of the figure , so we can mark this
02:35 angle as congruent to itself . Therefore , since two
02:41 of the angles of the smaller triangle are congruent to
02:45 two of the angles of the larger triangle . We
02:49 can say that yes , these triangles are similar by
02:53 the angle angle similarity postulate .
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