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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Mathematics
Chapter
Parabola

NTA Abhyas 2020 · Mathematics · Parabola

Let the tangents at points& P and R on the parabola y = x^ 2...

Let the tangents at points& PP and RR on the parabola y=x2y = x^{2} intersects at T.T . Tangent at point QQ (lies in between the points PP and RR ) on the parabola intersect PTPT and RTRT at AA and BB respectively. The value of TATP+TBTR\dfrac{TA}{TP} + \dfrac{TB}{TR}& is

Options

  1. A12\dfrac{1}{2}
  2. B11
  3. C22
  4. D44

Correct answer

B. 11

Step-by-step solution

Let,& P=P =\left({t}_{1}, {t}_{1}^{2}\right),Q = \left({t}_{2}, {t}_{2}^{2}\right) & R = \left({t}_{3}, {t}_{3}^{2}\right)<br />⇒ TATP=(t1+t32)−(t1+t22)(t1+t32−t1)=t3−t2t3−t1and</p><p>TBTR=t1−t2t1−t3=t2−t1t3−t1<br/>\dfrac{TA}{TP} = \left(\dfrac{{t}_{1} + {t}_{3}}{2}\right) - \left(\dfrac{{t}_{1} + {t}_{2}}{2}\right)\left(\dfrac{{t}_{1} + {t}_{3}}{2} - {t}_{1}\right) = \dfrac{{t}_{3} - {t}_{2}}{{t}_{3} - {t}_{1}} and</p><p>\dfrac{TB}{TR} = \dfrac{{t}_{1} - {t}_{2}}{{t}_{1} - {t}_{3}} = \dfrac{{t}_{2} - {t}_{1}}{{t}_{3} - {t}_{1}}<br />⇒ TATP+TBTR=t3−t2t3−t1+t2−t1t3−t1=t3−t1t3−t1=1\dfrac{TA}{TP} + \dfrac{TB}{TR} = \dfrac{{t}_{3} - {t}_{2}}{{t}_{3} - {t}_{1}} + \dfrac{{t}_{2} - {t}_{1}}{{t}_{3} - {t}_{1}} = \dfrac{{t}_{3} - {t}_{1}}{{t}_{3} - {t}_{1}} =1

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