Question

I need help find the value of x

Answer 1

From the picture, we see that there are two congruent sides. Therefore, following the Isosceles Triangle Theorem, if two sides in a triangle are congruent, then the angles opposite those sides are congruent. So, we know that the angles opposite of the congruent sides have an angle measure of x°. We are given the measure of the angle at the top vertex of 100°. Following the Triangle Sum Theorem, the three interior angles in a triangle must sum up to 180°. Therefore, we can create an Algebraic equation to solve for the two base angles that measure x°.

x+100+x=180

x=the base angle measures since they are congruent.

100+x+x=180

Community Property of Addition

100+2x=180.

Added x+x as like terms to = 2x.

100-100+2x=180-100

Subtraction of 100 from both sides to cancel it out and move it.

2x=80

Subtraction operation

2x/2=80/2

Divided by 2 to cancel it out on both sides and move it.

x=40°.

Therefore, the two base angles (angles opposite of the two congruent sides) are 40°.

2(40)+100=80+100=180.

So x=40