7th Class Mathematics Sample Paper Mathematics Sample Paper - 9

  • question_answer
    Find the value of \[\angle \]AOB in the given figure.

    Answer:

    In the given figure, ZAOB and ZCOB are the angles of linear pair.             So,         \[\angle AOB+\angle BOC=180{}^\circ \]           \[\left( 3x+{{10}^{^{0}}} \right)+\left( 2x-{{30}^{^{0}}} \right)={{180}^{^{0}}}\]           \[3x+10{}^\circ +2x-30{}^\circ =180{}^\circ \]          \[5x-20{}^\circ =180{}^\circ \]           \[5x=180{}^\circ +20{}^\circ \]     \[5x=200{}^\circ \]           \[x=\frac{200{}^\circ }{5}\]          Thus,  \[x\text{ }=\text{ }40{}^\circ \]                                                                                                               Now,           \[\angle AOB=3x+10{}^\circ \]       \[=\text{ }3\left( 40{}^\circ  \right)+10{}^\circ \] \[=\text{ }120{}^\circ +10{}^\circ \]


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