NIMCET 2023 — Mathematics PYQ
NIMCET | Mathematics | 2023A point P in the first quadrant, lies on y2=4ax, a>0, and keep a distance of 5a unit from its focus. Which of the following points lies on the locus of P?
Choose the correct answer:
- A.
(1,0)
- B.
(1,1)
(Correct Answer) - C.
(0,2)
- D.
(2,0)
(1,1)
Explanation
Step-by-step Derivation of the Locus
1. The focus of the parabola y2=4ax is known to be F(a,0).
2. Let the point P on the parabola be represented by its parametric coordinates, P(at2,2at).
3. The distance between point P and the focus F is given by the distance formula: PF=(at2−a)2+(2at−0)2.
4. It is given that this distance is 5a, so PF=5a.
5. Squaring both sides of the distance equation, (5a)2=(at2−a)2+(2at)2.
6. Expanding the terms, 25a2=a2(t2−1)2+4a2t2.
7. Dividing by a2 (since a > 0), 25=(t2−1)2+4t2.
8. Expanding the squared term, 25=t4−2t2+1+4t2.
9. Simplifying the equation, 25=t4+2t2+1.
10. This can be rewritten as 25=(t2+1)2.
11. Taking the square root of both sides, 25=(t2+1)2, which gives 5=t2+1.
12. Solving for t2, t2=5−1=4.
13. Since P is in the first quadrant, both its x and y coordinates must be positive. This implies t > 0, so t=4=2.
14. Substituting t=2 back into the coordinates of P, x=a(22)=4a and y=2a(2)=4a.
15. Therefore, the point P is (4a,4a).
16. The locus of P is the set of all such points (4a,4a) for any a > 0.
17. The question asks which of the given points lies on this locus. This means checking which point has equal x and y coordinates.
18. Examining the options:
• (a) (1,0): x=y.
• (b) (1,1): x=y. This point lies on the locus if a=41.
• (c) (0,2): x=y.
• (d) (2,0): x=y.
Final Answer
The point that lies on the locus of P is (1,1).

