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Algebra Level 2

Suppose that m m is a real number such that the two graphs 2 x 1 + y = 2 and y = m x + 5 m 2 2|x-1|+|y|=2\ \text { and } y=mx+5m-2 intersect. What is the sum of the maximum and minimum values of m ? m?

3 4 \frac{3}{4} 1 2 \frac{1}{2} 2 3 \frac{2}{3} 4 5 \frac{4}{5}

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1 solution

Tom Engelsman
Nov 22, 2020

The plot of 2 x 1 + y = 2 2|x-1| + |y| =2 is a rhombus:

with vertices at ( x , y ) = ( 0 , 0 ) ; ( 1 , 2 ) ; ( 1 , 2 ) ; ( 2 , 0 ) (x,y) = (0,0); (1,-2); (1,2); (2,0) . Solving for m m gives m ( x , y ) = y + 2 x + 5 m(x,y) = \frac{y+2}{x+5} , and if we substitute the aforementioned points we obtain:

m ( 0 , 0 ) = 2 5 ; m ( 1 , 2 ) = 0 ; m ( 1 , 2 ) = 2 3 ; m ( 2 , 0 ) = 2 7 . m(0,0) = \frac{2}{5}; m(1,-2) = 0; m(1,2) = \frac{2}{3}; m(2,0) = \frac{2}{7}.

Hence, m M I N + m M A X = 0 + 2 3 = 2 3 . m_{MIN} + m_{MAX} = 0 + \frac{2}{3} = \boxed{\frac{2}{3}}.

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