secant squared theta minus tan squared theta + tan theta / secant theta is equals to sin theta + cos theta​

The general form of the quetion of a circle is ax^2+by^2+cx+dy+e=0 where a=b=0 if the circle has a radius of three units and the center lies on the y axis which set of values of a, b, c, d, and e might correspond to the circle

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State one method by which you can recognize a perfect square trinomial.