7th Class Mathematics The Triangle and its Properties

  • question_answer 6)
    Find the value of the unknown \[x\] in the following diagrams: (i)     (ii)       (iii)     (iv) (v)   (vi)                

    Answer:

                    (i)            \[x+{{50}^{o}}+{{60}^{o}}={{180}^{o}}\]               \[\left| \text{By the angle}-\text{sum property of a triangle} \right.\] \[\Rightarrow \]               \[x+{{110}^{o}}={{180}^{o}}\] \[\Rightarrow \]               \[x={{180}^{o}}-{{110}^{o}}\] \[\Rightarrow \]               \[x={{70}^{o}}\] (ii)           \[x+{{90}^{o}}+{{30}^{o}}={{180}^{o}}\]                \[\left| \text{By the angle}-\text{sum property of a triangle} \right.\] \[\Rightarrow \]               \[x+{{120}^{o}}={{180}^{o}}\]                 \[\Rightarrow \]               \[x={{180}^{o}}-{{120}^{o}}\]                 \[\Rightarrow \]               \[x={{60}^{o}}\] (iii)        \[x+{{30}^{o}}+{{110}^{o}}={{180}^{o}}\]                                              \[\left| \text{By the angle}-\text{sum property of a triangle} \right.\] \[\Rightarrow \]               \[x+{{140}^{o}}={{180}^{o}}\] \[\Rightarrow \]               \[x={{180}^{o}}-{{140}^{o}}\] \[\Rightarrow \]               \[x={{40}^{o}}\] (iv)         \[x+x+{{50}^{o}}={{180}^{o}}\] \[\left| \text{By the angle}-\text{sum property of a triangle} \right.\] \[\Rightarrow \]               \[2x+{{50}^{o}}={{180}^{o}}\] \[\Rightarrow \]               \[2x={{180}^{o}}-{{50}^{o}}\] \[\Rightarrow \]               \[2x={{130}^{o}}\] \[\Rightarrow \]               \[x=\frac{{{130}^{o}}}{2}\] \[\Rightarrow \]               \[x={{65}^{o}}\] (v)          \[x+x+x={{180}^{o}}\] \[\left| \text{By the angle - sum property of a triangle} \right.\] \[\Rightarrow \]               \[3x={{180}^{o}}\]                 \[\Rightarrow \]               \[x=\frac{{{180}^{o}}}{3}\]                 \[\Rightarrow \]               \[x={{60}^{o}}\] (vi)         \[x+2x+{{90}^{o}}={{180}^{o}}\] \[\left| \text{By the angle - sum property of a triangle} \right.\] \[\Rightarrow \]               \[3x+{{90}^{o}}={{180}^{o}}\]                 \[\Rightarrow \]               \[3x={{180}^{o}}-{{90}^{o}}\]                 \[\Rightarrow \]               \[3x={{90}^{o}}\]                 \[\Rightarrow \]               \[x=\frac{{{90}^{o}}}{3}\] \[\Rightarrow \]               \[x={{30}^{o}}\]


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