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Zorluk: ZorSystems of Linear Equations
A financial analyst models a company's weekly metrics using three variables—revenue RR, operating cost CC, and advertising expenditure AA, measured in thousands of dollars. The metrics satisfy the following system of linear equations, where kk is a real constant:
4R3C+2A=18R+5C6A=145R+2C4A=k\begin{aligned} 4R - 3C + 2A &= 18 \\ R + 5C - 6A &= 14 \\ 5R + 2C - 4A &= k \end{aligned}
If this system of linear equations is consistent (has at least one solution), what is the value of kk?
  1. A
    4
  2. B
    16
  3. 32Cevap
  4. D
    -32
  5. E
    252

Cevap

32
Adding the left-hand sides of the first two equations yields (4R3C+2A)+(R+5C6A)=5R+2C4A(4R - 3C + 2A) + (R + 5C - 6A) = 5R + 2C - 4A, which is identical to the left-hand side of the third equation. For the linear system to have at least one solution (to be consistent), the right-hand side constant must satisfy the exact same linear combination: k=18+14=32k = 18 + 14 = 32.

Adım Adım Çözüm

1
Examine the linear combination of the left-hand sides of the first two equations
(4R3C+2A)+(R+5C6A)=5R+2C4A(4R - 3C + 2A) + (R + 5C - 6A) = 5R + 2C - 4A
Observing that the sum of the coefficients of the first two equations matches the left-hand side of the third equation.
2
Apply the condition for system consistency
Right-hand side of Equation 3 must equal Right-hand side of Equation 1 + Right-hand side of Equation 2
For a system with linearly dependent left-hand sides to be consistent, the same linear combination must hold for the right-hand constants.
3
Calculate the value of kk
k=18+14=32k = 18 + 14 = 32
Adding the constants from the right-hand side of the first two equations gives the consistent value for kk.

Anahtar Kavram

Consistency and Linear Dependence in Systems of Linear Equations
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