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A conic has equation $$ay^2+bx=0$$

where $a=5$ and $b=-315$. If the focus point is at $(F, 0)$ then what is the value of $F$ to 2 decimal places?

Hi, I want to check if i have applied the correct formula to solve this question. My answer is $F=15.75$.

This is my working:

$5y^2 - 315x =0$

$5y^2 = 315x$ (bringing $-315$ from LHS to RHS)

$y^2 = 315x$ divided by $5$

$y^2 = 63x$

$y^2 = 4ac$ (Equation of parabola in in standard position, where $a >0$)

$a = 63$ divided by $4$

$a = 15.75$

Hakim
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Adma
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  • When you divide by $5$, or any number, do it in one step, never two steps like you did. – user88595 Apr 27 '14 at 11:32
  • So the answer 15.75 is incorrect? – Adma Apr 27 '14 at 11:38
  • It is correct. What I meant is avoid writing "divided by 5". Either do it and write $63$ on the next line or $\frac{315x}{5}$ but the way you did it is unclear. Same goes with the last step, write "$a = 63/4$" instead of "$a = 63$ divided by 4" – user88595 Apr 27 '14 at 16:32

1 Answers1

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Your solution of $F=15.75$ is correct. Hence that if you are able to plug in the correct values in the right places, the equations came be solved by basic Algebra techniques you have learned. Which would solve for $F$.