Page 93 - Mathematics Class - XI

3. On the other sheets sketch the graphs (x + 3) + y = 25.
2
2

Fig. (b)

4. On the third sheet sketch the curve xy = 9 (rectangular hyperbola)

Fig. (c)

DEMONSTRATION
1. Take first sheet on which, the graph of the circle x + y = 25
2
2
2. Take a point A (4, 3) on the circle.
3. With the help of a set square, place a wire in the direction of OA and other perpendicular to OA at the
point A to meet x-axis at a point (say P).
4. Measure the angle between the wire and the positive direction of x-axis at P (say q).
5. Then find tan q (with the help of trigonometric tables)

dy −x
Now, x + y = 25 ⇒ y = 25 − x 2 ⇒ =
2
2
dx 25 − x 2
dy  dy
Find at the point (4, 3) and verify that   at (4, 3) = tan q.
dx  dx
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