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Algebra Difficulty 4.9 AIME Find the answer

Find the real solutions of (2x+1)(3x+1)(5x+1)(30x+1)=10(2 x+1)(3 x+1)(5 x+1)(30 x+1)=10.

A number or a short expression. Spacing and $ signs are ignored.

Solution

(2x+1)(3x+1)(5x+1)(30x+1)=[(2x+1)(30x+1)][(3x+1)(5x+1)]=(60x2+32x+1)(15x2+8x+1)=(4y+1)(y+1)=10(2 x+1)(3 x+1)(5 x+1)(30 x+1)=[(2 x+1)(30 x+1)][(3 x+1)(5 x+1)]=\left(60 x^{2}+32 x+1\right)\left(15 x^{2}+8 x+1\right)=(4 y+1)(y+1)=10, where y=15x2+8xy=15 x^{2}+8 x. The quadratic equation in yy yields y=1y=1 and y=94y=-\frac{9}{4}. For y=1y=1, we have 15x2+8x1=015 x^{2}+8 x-1=0, so x=4±3115x=\frac{-4 \pm \sqrt{31}}{15}. For y=94y=-\frac{9}{4}, we have 15x2+8x+9415 x^{2}+8 x+\frac{9}{4}, which yields only complex solutions for xx. Thus the real solutions are 4±3115\frac{-4 \pm \sqrt{31}}{15}.

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Source: Omni-MATH, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.