BFC - we have two base angles that are the same which means this must be an isosceles triangle so BC - must be the same as FC so that was kinda cool we just used the transversal and the alternate interior angles to show that these are isosceles and that BC and FC are the same thing and that could be useful because we know that we want to - we have a feeling that this triangle and this triangle are going to be similar we haven't proven it yet but how will that help us get something about BC up here? but we just showed that BC and FC are the same thing so this is going to be the same thing as what we wanna prove it and if we can prove that FC - the ratio of AB to AD is the same thing as the ratio of FC to CD were gonna be there because BC - we just showed - is equal to