Find the real solutions of (2x+1)(3x+1)(5x+1)(30x+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, where y=15x2+8x. The quadratic equation in y yields y=1 and y=−49. For y=1, we have 15x2+8x−1=0, so x=15−4±31. For y=−49, we have 15x2+8x+49, which yields only complex solutions for x. Thus the real solutions are 15−4±31.
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