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There are three consecutive positive integers such that the sum of the square of the first and the product of the other two is 154. What are the integers ?

Quadratic Equations

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Answer

Let the numbers be x , x + 1 , x + 2.

Given, sum of the square of the first and the product of the other two is = 154

x2+(x+1)(x+2)=154x2+(x2+2x+x+2)=1542x2+3x+2154=02x2+3x152=02x2+19x16x152=0x(2x+19)8(2x+19)=0(x8)(2x+19)=0x8=0 or 2x+19=0x=8 or x=192\Rightarrow x^2 + (x + 1)(x + 2) = 154 \\[1em] \Rightarrow x^2 + (x^2 + 2x + x + 2) = 154 \\[1em] \Rightarrow 2x^2 + 3x + 2 - 154 = 0 \\[1em] \Rightarrow 2x^2 + 3x - 152 = 0 \\[1em] \Rightarrow 2x^2 + 19x - 16x - 152 = 0 \\[1em] \Rightarrow x(2x + 19) - 8(2x + 19) = 0 \\[1em] \Rightarrow (x - 8)(2x + 19) = 0 \\[1em] \Rightarrow x - 8 = 0 \text{ or } 2x + 19 = 0 \\[1em] x = 8 \text{ or } x = -\dfrac{19}{2}

Since the integers are positive hence , x ≠ 192-\dfrac{19}{2}

∴ x = 8 , x + 1 = 9 , x + 2 = 10.

Hence , the required numbers are 8, 9, 10.

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