00:01
So what do i have here? well, i have a smaller triangle, and then i have a larger triangle, and i know that these sides are parallel.
00:10
Since these are parallel, i can use the triangle proportionality theorem.
00:18
What does the triangle proportionality theorem say? well, i know that they both share an angle here, and then because they're parallel corresponding angles are equal.
00:27
So by angle -angle similarity, these triangles are similar.
00:30
So what i can do is set up a proportion between these two sides.
00:35
So i could do the smaller length, smaller triangle, 15 over my question mark, equals length of the longer side, which is 15 plus 6 or 21, over question mark plus 10.
00:50
Then what i could do is cross multiply to solve this.
00:53
So this will be 15 times, let's call this x instead of question mark, times that whole quantity, and then 21 times x...