Maths Olympiad Prep

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Algebra Difficulty 2.5 Junior Find the answer Canada

The product of the roots of the equation (x4)(x2)+(x2)(x6)=0(x-4)(x-2)+(x-2)(x-6)=0 is

Pick one

Solution

Solution 1

Since the two terms have a common factor, then we factor and obtain (x2)((x4)+(x6))=0(x-2)((x-4)+(x-6))=0.

This gives (x2)(2x10)=0(x-2)(2x-10)=0.

Therefore, x2=0x-2=0 (which gives x=2x=2) or 2x10=02x-10=0 (which gives x=5x=5).

Therefore, the two roots of the equation are x=2x=2 and x=5x=5. Their product is 10.

Solution 2

We expand and then simplify the left side: (x4)(x2)+(x2)(x6)=0(x26x+8)+(x28x+12)=02x214x+20=0\begin{aligned} (x-4)(x-2) + (x-2)(x-6) & = & 0 \\ (x^2-6x+8) + (x^2 - 8x + 12) & = & 0 \\ 2x^2 - 14x + 20 & = & 0 \end{aligned} Since the product of the roots of a quadratic equation of the form ax2+bx+c=0ax^2+bx+c=0 with a0a \neq 0 is ca\dfrac{c}{a}, then the product of the roots of the equation 2x214x+20=02x^2-14x+20 =0 is 202=10\dfrac{20}{2}=10.

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.