Question : If $ax^{2}+bx+c=a(x-p)^{2}$, then the relation among $a, b ,$ and $c$ would be:
Option 1: $abc=1$
Option 2: $b^{2}=ac$
Option 3: $b^{2}=4ac$
Option 4: $2b=a+c$
Correct Answer: $b^{2}=4ac$
Solution :
$ax^{2}+bx+c=a(x-p)^{2}$
⇒ $ax^{2}+bx+c=a(x^{2}-2px+p^{2})$
⇒ $ax^{2}+bx+c=ax^{2}-2apx+ap^{2}$
Comparing the corresponding coefficients, we get,
$ b = -2ap$-----------(i)
$ c = ap^2$---------------(ii)
Squaring equation (i), we have,
⇒ $ b^2 = 4a^2p^2 $
⇒ $ p^2 = \frac{b^2}{4a^2}$-------------(iii)
Substituting (iii) in (ii), we get,
⇒ $ c = a×\frac{b^2}{4a^2}$
$\therefore b^2 = 4ac$
Hence, the correct answer is $ b^2 = 4ac$.
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