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Statement 1 : An equation of a common tangent to the parabola y2 = 163 x and the ellipse 2x2 + y2 = 4 is y = 2x + 23
Statement 2 : If the line y = mx + 43/m, (m ≠ 0) is a common tangent to the parabola y2 = 163x and the ellipse 2x2 + y2 = 4, then m satisfies m4 + 2m2 = 24.
(a) Statement 1 is true, Statement 2 is true; Statement 2 is not a correct explanation for Statement 1.
(b) Statement 1 is true, Statement 2 is false.
(c) Statement 1 is false, Statement 2 is true.
(d) Statement 1 is true, Statement 2 is true; Statement 2 is a correct explanation for Statement 1.

1 Answer

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Best answer

(d) : Statement 1 :

\(y^2=16\sqrt3x,\) 

Therefore, the equation of tangent to the given parabola is \(y=mx+\frac{4\sqrt3}{m}\) ......(1)

\(\frac{x^2}{2}+\frac{y^2}{4}=1,\) 

Therefore, the equation of tangent to the given ellipse is \(x=m_1y+\sqrt{4m_1^2+2}\)

\(\Rightarrow y=\frac{x}{m_1}-\sqrt{4+\frac{2}{m_1^2}}\)   .....(2)

Since, equations (1) and (2) represents common tangents to both ellipse and parabola.

Therefore, by comparing equations (1) and (2), we obtain
\(m=\frac{1}{m_1}\)

And

\((\frac{4\sqrt3}{m})^2=\bigg(-\sqrt{4+\frac{2}{m_1^2}}\bigg)^2\)

\(\Rightarrow \frac{48}{m^2}=4+\frac{2}{m_1^2}\)\(=4+2m^2\) (\(\because\, m=\frac{1}{m_1}\))

\(\Rightarrow\frac{24}{m^2}=2+m^2\)

\(\Rightarrow m^4+2m^2-24=0...(3)\)

\(\Rightarrow(m^2+6)(m^2-4)=0\) 

\(\Rightarrow m=\pm2\)

 Statement 2:

If \(y=mx+\frac{4\sqrt3}{m}\) is a common tangent

to \(y^2=16\sqrt3x\) and ellipse \(2x^2+y^2=4,\) then m

satisfies \(m^4+2m^2-24=0\).    (From equation (3))

Hence, statement (2) is true.

Now, by putting m=2 in equation (1), we get the common tangent which is 
\(y=2x+\frac{4\sqrt3}{2}\) 

\(\Rightarrow y=2x+{2\sqrt3}\)

Hence, statement (1) is true.

Thus, statement (2) is a correct explanation for statement (1).

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