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Miscellaneous Exercise 2(I) · Q108

Q.If the tangent at (1,1)(1, 1) on y2=x(2−x)2y^2 = x(2 - x)^2 meets the curve again at PP then PP is (A) (4,4)(4, 4) (B) (−1,2)(-1, 2) (C) (3,6)(3, 6) (D) (94,38)\left(\dfrac94, \dfrac38\right)

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Differentiating y2=x(2−x)2y^2=x(2-x)^2 implicitly: 2yy′=(2−x)2+x⋅2(2−x)(−1)=(2−x)[(2−x)−2x]=(2−x)(2−3x)2y y'=(2-x)^2+x\cdot2(2-x)(-1)=(2-x)[(2-x)-2x]=(2-x)(2-3x).

At (1,1)(1,1): y′=(2−1)(2−3)2(1)=(1)(−1)2=−12y'=\dfrac{(2-1)(2-3)}{2(1)}=\dfrac{(1)(-1)}{2}=-\dfrac12.

Tangent: y−1=−12(x−1)⇒2y−2=−(x−1)⇒x+2y−3=0⇒y=3−x2y-1=-\dfrac12(x-1) \Rightarrow 2y-2=-(x-1) \Rightarrow x+2y-3=0 \Rightarrow y=\dfrac{3-x}{2}.

Substituting into the curve: (3−x2)2=x(2−x)2⇒(3−x)2=4x(2−x)2\left(\dfrac{3-x}{2}\right)^2=x(2-x)^2 \Rightarrow (3-x)^2=4x(2-x)^2.

Expanding: 9−6x+x2=4x(4−4x+x2)=16x−16x2+4x39-6x+x^2 = 4x(4-4x+x^2)=16x-16x^2+4x^3, so 4x3−17x2+22x−9=04x^3-17x^2+22x-9=0. …

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