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Prove that equilateral triangles are equiangular?
Statement Reason1. triangle ABC is equilateral..............................................given2. AC is congruent to BC;AB is congruent to AC........................................definition of equilateral3. angle A is congruent to angle B;and B is congruent to angle C.............................Isosceles Theorem4. angle A is congruent to angle C..................Transitive Property of Congruence5. triangle ABC is equiangular...............................Definition of equiangular
If measure reflex angle ABC equals 240 then measure angle ABC equals?
The sum of the two angles is 360. So angle ABC = 120 degrees.
What must A measure in order for ABC to be isosceles?
Are you talking about the angle A. If you are then at what point of the triangle is the angle A.
How do you prove the isosceles triangle theorem?
The isosceles triangle theorem states: If two sides of a triangle are congruent, then the angles opposite to them are congruent Here is the proof: Draw triangle ABC with side AB congruent to side BC so the triangle is isosceles. Want to prove angle BAC is congruent to angle BCA Now draw an angle bisector of angle ABC that inersects side AC at a point P. ABP is congruent to CPB because ray BP is a bisector of angle ABC Now we know side BP is congruent to side BP. So we have side AB congruent to BC and side BP congruent to BP and the angles between them are ABP and CBP and those are congruent as well so we use SAS (side angle side) Now angle BAC and BCA are corresponding angles of congruent triangles to they are congruent and we are done! QED. Another proof: The area of a triangle is equal to 1/2*a*b*sin(C), where a and b are lengths of adjacent sides, and C is the angle between the two sides. Suppose we have a triangle ABC, where the lengths of the sides AB and AC are equal. Then the area of ABC = 1/2*AB*BC*sin(B) = 1/2*AC*CB*sin(C). Canceling, we have sin(B) = sin(C). Since the angles of a triangle sum to 180 degrees, B and C are both acute. Therefore, angle B is congruent to angle C. Altering the proof slightly gives us the converse to the above theorem, namely that if a triangle has two congruent angles, then the sides opposite to them are congruent as well.
What are congruence theorems and postulates?
If the sides AB, BC and CA of triangle ABC correspond to the sides DE, EF and FD of triangle DEF, then the two triangles are congruent if:AB = DE, BC = EF and CA = FD (SSS)AB = DE, BC = EF and angle ABC = angle DEF (SAS)AB = DE, angle ABC = angle DEF, angle BCA = angle EFD (ASA)If the triangles are right angled at A and D so that BC and EF are hypotenuses, then the triangles are congruent ifBC = EF and AB = DE (RHS)BC = EF and angle ABC = angle DEF (RHA).
