Algebra problem 001

Level 2

Solve for x x when the radius of a cone equals x x , the height equals x 7 x - 7 and the slant height equals x + 1 x + 1 .

193 12, or 13 12, or 4 16, or 10 12

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1 solution

Blan Morrison
Feb 8, 2018

We can put this problem into the 2nd dimension and solve for x x :

Using the Pythagorean Theorem, we can set up an equation: x 2 + ( x 7 ) 2 = ( x + 1 ) 2 x^2+(x-7)^2=(x+1)^2 And simplify into a trinomial that equals 0: x 2 16 x + 48 = 0 x^2-16x+48=0 Then, we can factor the trinomial into 2 binomials to solve for x x : ( x 12 ) ( x 4 ) = 0 (x-12)(x-4)=0 If one of the factors is 0, then the entire equation is true. Therefore, we can set each of the binomials equal to zero: x 12 = 0 ; x 4 = 0 x-12=0;~x-4=0 Solving for both equations, we get 2 positive solutions of 12 and 4 \boxed{12~\text{and}~4} .

Note : 4, in the real world, would not be a valid solution. This is because you would have a height of -3, which is impossible.

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