Question

Find angle measure GRS if QRS=179 and QRG= 105

Answer 1

75°

Explanation:

While it may appear that QRS is a straight line, it is not so since m∠QRS = 179° and if it was a straight line, it would be 180°

The figure actually represents three rays with endpoint at R

The three rays are RQ, RS and RG

Draw another ray RT with endpoint at R and opposite to ray RG. Opposite rays have angles that add up to 180°

Therefore m∠GRT = 180°

m∠SRT = m∠QRG since they are opposite angles

Since m∠QRG = 105°, therefore m∠SRT = 105°

m∠GRS + m∠SRT=180° since these angles are formed by two opposite rays

Substituting we get
m∠GRS + 105 = 180

m∠GRS = 180-105 = 75°

Answer 2

∠ GRS = 74°

Explanation:

∠ GRS + ∠ QRG = ∠ QRS , that is

∠ GRS + 105° = 179° ( subtract 105° from both sides )

∠ GRS = 74°