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Olympiad workbook
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Olympiad workbook
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IOQM
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Quadratic Equation

Olympiad workbook · IOQM · Quadratic Equation

Let t be the area of a regular pentagon with each side equal to 1 ....

Let tt be the area of a regular pentagon with each side equal to 1 . Let P(x)=0P(x)=0 be the polynomial equation with least degree, having integer coefficients, satisfied by x=tx=t and the gcd of all the coefficients equal to 1 . If MM is the sum of the absolute values of the coefficients of P(x)P(x). What is the integer closest to M?(sin⁡18∘=(5−1)/2)\sqrt{\mathrm{M}} ?\left(\sin 18^{\circ}=(\sqrt{5}-1) / 2\right).

Correct answer

16

Step-by-step solution

\text { Area of regular pentagon }=\frac{a^2 n}{4 \tan \left(\frac{180}{n}\right)} n⇒n \Rightarrow No. of sides a⇒\mathrm{a} \Rightarrow Length of side ∴\therefore For regular pentagon by side length 1 ,  Area (t)=54tan⁡36∘=54(0.73)=1.71\begin{aligned} \text { Area }(t) & =\frac{5}{4 \tan 36^{\circ}} \\ & =\frac{5}{4(0.73)} \\ & =1.71 \end{aligned} Now, P(1.71)=0\mathrm{P}(1.71)=0 to be found with least degree and integer coefficient soon that gcd of all coefficient is 1 . Let x=1.71\quad \mathrm{x}=1.71 100x=171100 x=171 ∴P(x)=100x−171=0\therefore \mathrm{P}(\mathrm{x})=100 \mathrm{x}-171=0 is the polynomial which satisfied all the conditions. ∴m=100+171=271∴ m=16.46∴ Nearest integer =16\begin{aligned} & \therefore \mathrm{m}=100+171=271 \\ & \therefore \sqrt{\mathrm{~m}}=16.46 \\ & \therefore \text { Nearest integer }=16 \end{aligned} But this question can have multiple solutions as student can take \tan 36 as 0.72,0.7260.72,0.726 or even 0.7. Every time we will get different answers. So this question should be Bonus.
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