The system of equations 2x + 3y = 8 and (A + 7)x + (B2 – 22)y = 24B, where A and B are real numbers, has infinitely many solutions for x and y. What is the sum of the maximum and minimum values of AB?
Question
The system of equations 2x + 3y = 8 and (A + 7)x + (B2 – 22)y = 24B, where A and B are real numbers, has infinitely many solutions for x and y. What is the sum of the maximum and minimum values of AB?
Solution 1
For a system of linear equations to have infinitely many solutions, the two equations must be proportional to each other. This means that the coefficients of the variables in the first equation must be proportional to the coefficients of the variables in the second equation.
From the first equation, we have the coefficients 2 and 3 for x and y respectively. From the second equation, we have the coefficients (A + 7) and (B2 – 22) for x and y respectively.
Setting up the proportions, we get:
2/(A + 7) = 3/(B2 – 22)
Cross multiplying gives us:
2(B2 – 22) = 3(A + 7)
Expanding this gives us:
2B2 - 44 = 3A + 21
Rearranging terms gives us:
3A - 2B2 = -65 -----(1)
From the second equation, we also have the constant terms 8 and 24B. Setting up the proportion for the constant terms, we get:
8/24B = 1
Solving for B gives us:
B = 1/3 -----(2)
Substituting B = 1/3 into equation (1) gives us:
3A - 2*(1/3)^2 = -65
Solving for A gives us:
A = -22
Therefore, the values of A and B are -22 and 1/3 respectively. The product AB is -22*(1/3) = -22/3.
Since A and B are constants, the maximum and minimum values of AB are the same, which is -22/3. Therefore, the sum of the maximum and minimum values of AB is -22/3 + -22/3 = -44/3.
Solution 2
For a system of equations to have infinitely many solutions, the equations must be proportional to each other. This means that the coefficients of the variables in the first equation must be proportional to the coefficients of the variables in the second equation.
From the first equation, we have 2x + 3y = 8.
From the second equation, we have (A + 7)x + (B2 – 22)y = 24B.
Comparing the coefficients of x in both equations, we get 2/(A+7) = 1. Solving for A, we get A = 2 - 7 = -5.
Comparing the coefficients of y in both equations, we get 3/(B2 - 22) = 1. Solving for B, we get B2 - 22 = 3, which gives B2 = 25. Therefore, B = ±5.
So, the possible values of AB are -55 = -25 and -5-5 = 25.
The sum of the maximum and minimum values of AB is 25 + (-25) = 0.
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