How many triangles can be drawn having its angles $45°, 64°$ and $72°$?
Give reason for your answer.

In the given figure, find the value of $x$ for which the lines $l$ and $m$ are parallel.

In the given figures, which of the two lines are parallel and why?

In the given figure, $OD$ is the bisector of $\angle AOC, OE$ is the bisector of$\angle BOC$ and $OD\perp OE$. Show that the points $A,O$and $B$ are collinear.

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In the given figure, $\angle 1=60°$ and $\angle 6=120°$. Show that the lines m and n are parallel.

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