Question

In a given triangle ABC, angleA + angleB = 105 o and angleB + angleC = 120 o . What is the measure of angleB ??

Answer 1

sum of angles of a triangle= 180°
A+B=105°
B+C=120°
 A+B+B+C=225°
We know that A+B+C=180°
..............................................
B= 225°-180°= 45°
Therefore angle B is 45°

Answer 2

<A+<B=105-----(1)
<B+<C=120-----(2).

sum of angles in a triangle =180degree

do the sum of (1) and (2)

<A+<B +<B+<C=105+120

(<A+<B+<C)+<B=225

180+<B =225

<B =225 -180

<B=45