8th Class Mathematics Understanding Quadrilaterals

  • question_answer 15)
                    Consider the following parallelograms. Find the degree values of the unknowns \[x,\,y,\,z\]. (i) (ii) (iii)

    Answer:

                    (i) \[y={{100}^{o}}\] | Opposite angles of a parallelogram are equal \[x+{{100}^{o}}={{180}^{o}}\] Adjacent angles in a parallelogram are supplementary \[\Rightarrow \]               \[x={{180}^{o}}-{{100}^{o}}\] \[\Rightarrow \]               \[x={{80}^{o}}\] \[z=x={{80}^{o}}\] (ii) \[x+{{50}^{o}}={{180}^{o}}\] |Adjacent angles in a parallelogram are supplementary \[\Rightarrow \]               \[x={{180}^{o}}-{{50}^{o}}={{130}^{o}}\]                 \[y=x={{130}^{o}}\] |The opposite angles of a parallelogram are of equal measure \[{{180}^{o}}-z={{50}^{o}}\] \[\Rightarrow \]               \[z={{180}^{o}}-{{50}^{o}}={{130}^{o}}\] (iii) \[x=90{}^\circ \] \[x+y+{{30}^{o}}=~{{180}^{o}}\] | By angle sum property of a triangle \[\Rightarrow \]               \[{{90}^{o}}+y+30={{180}^{o}}\] \[\Rightarrow \]               \[{{120}^{o}}+y={{180}^{o}}\] \[\Rightarrow \]               \[y={{180}^{o}}-{{120}^{o}}={{60}^{o}}\] \[z+{{30}^{o}}+{{90}^{o}}={{180}^{o}}\] | By angle sum property of a triangle \[\Rightarrow \]               \[z={{60}^{o}}\] (iv) \[y={{80}^{o}}\] \[x+{{80}^{o}}={{180}^{o}}\] Adjacent angles in a parallelogram are supplementary \[\Rightarrow \]               \[x={{180}^{o}}-{{80}^{o}}\] \[\Rightarrow \]               \[x={{100}^{o}}\] \[{{180}^{o}}-z+{{80}^{o}}={{180}^{o}}\] |Linear pair property and adjacent angles in a parallelogram are supplementary. \[\Rightarrow \]          \[z={{80}^{o}}\] (v)           \[={{112}^{o}}\] |Opposite angles of a parallelogram are equal \[x+y+{{40}^{o}}={{180}^{o}}\] | By angle sum property of a triangle \[\Rightarrow \]               \[x+{{112}^{o}}+{{40}^{o}}={{180}^{o}}\] \[\Rightarrow \]               \[x+{{152}^{o}}={{180}^{o}}\] \[\Rightarrow \]               \[x={{180}^{o}}-{{152}^{o}}\] \[\Rightarrow \]               \[x={{28}^{\text{o}}}\] \[\Rightarrow \]               \[z=x={{28}^{o}}\]           | Alternate angle


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