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Question

find the area of the triangle formed by the positive x axis and the tangent and normal to the curve x^2 + y^2 =9 at(2,√5).

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Solution

The curve you will get from that EQ. Is a a circle from centre with radius 3.

The equation of tangent from the point is

2x+(√5)y=9

and the equation of normal is

(√5)x =2y (passing through origin)

Now we know two points of the triangle.. i.e (0,0) and (2,√5) and the third point would be the POI of x axis(y=0) and the tangent.

Puting y=0 in the equation of tangent, we get x=9/2.

So now we have all three points. You can use these co-ordinates to find the area of triangle (by various formulas) or just use the simple formula of b*h/2

For the triangle formed by point A(0,0), B(9/2,0) and C(2,√5). let the base be AB. Also the y co-ordinate of C would then be the height.

Applying the formula for area of triangle

Area=b*h/3

=(9/2)*(√5)*(1/2)

=9√5/4


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