The first one is isosceles because it has two side lengths that are the same, C. The missing angle measure is 35° because all of them together should add up to 180° and 105+40+35=180, A. The possible lengths for the third triangle e are in between 7, and 17. This is because the possible side lengths are in between adding the two side lengths together, (12+5=17) and subtracting the littler side by the bigger side. (12-5=7)
