PLEASE HELP ME ANSWER THIS CORRECTLY! THIS IS MY 1st PART OF EXAM! PLEASE PLEASE PLEASEE!

A plus B equals D

Step-by-step explanation:

Because if you add the angles of A and B together, it will always equal D, or the third corner, because if it didn't it wouldn't be a triangle. Sorry, isn't the best explanation but that's all I've got lol.

As triangle "angles" that add up to 180, I will use the angle as an example, if ∠a is 80° and ∠b is 40°. ∠80 + ∠40 = ∠120.

For a triangle, the total angle is 180° and ∠c would be 60°. The same goes to supplementary which is 180° striaght line, if ∠c is 60° then ∠d is 120°. In conclusion as of my explanation, ∠a + ∠b = ∠d is that triangle and supplementary have the same total angle of 180°.

b. an equilateral triangle inscribed in a circle

step-by-step explanation:

we are given the figure of two circles having a triangle inside.

now, we know that,

"when a figure is lying inside an another figure, then the outside figure is known as circumscribed figure and the figure lying inside is referred to as the inscribed figure".

as we see that, the circles are containing the triangle completely.

thus, the circles are the circumscribed figures and the triangle is the inscribed figure.

hence, we get, 'an equilateral triangle is inscribed in a circle'.

d. vertex

step-by-step explanation: