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Solve the following system of linear equations: 2a + 3b + 4c = 11, a + 5b + 7c = 15, a + 11b + 13 = 25

Mathematics

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Answer

a=175109a = \frac{175}{109}

b=103109b = \frac{103}{109}

c=135109c = \frac{135}{109}

Step-by-step solution

6 steps

Here's the solution to the system of equations.

The given system of equations is:

  1. 2a+3b+4c=112a + 3b + 4c = 11
  2. a+5b+7c=15a + 5b + 7c = 15
  3. a+11b+13=25a + 11b + 13 = 25
  1. Simplify Equation (3).

    Subtract 13 from both sides of Equation (3):

    a+11b=25−13a + 11b = 25 - 13 a+11b=12(Equation 3 simplified)a + 11b = 12 \quad (\text{Equation 3 simplified})
  2. Express aa in terms of bb from the simplified Equation (3).

    a=12−11b(Equation 4)a = 12 - 11b \quad (\text{Equation 4})
  3. Substitute Equation (4) into Equation (1) and Equation (2) to eliminate aa.

    Substitute a=12−11ba = 12 - 11b into Equation (1):

    2(12−11b)+3b+4c=112(12 - 11b) + 3b + 4c = 11 24−22b+3b+4c=1124 - 22b + 3b + 4c = 11 −19b+4c=11−24-19b + 4c = 11 - 24 −19b+4c=−13(Equation 5)-19b + 4c = -13 \quad (\text{Equation 5})

    Substitute a=12−11ba = 12 - 11b into Equation (2):

    (12−11b)+5b+7c=15(12 - 11b) + 5b + 7c = 15 12−6b+7c=1512 - 6b + 7c = 15 −6b+7c=15−12-6b + 7c = 15 - 12 −6b+7c=3(Equation 6)-6b + 7c = 3 \quad (\text{Equation 6})
  4. Solve the system of two equations (Equation 5 and Equation 6) for bb and cc.

    We have: 5) −19b+4c=−13-19b + 4c = -13 6) −6b+7c=3-6b + 7c = 3

    Multiply Equation (5) by 7 and Equation (6) by 4 to eliminate cc:

    7(−19b+4c)=7(−13)  ⟹  −133b+28c=−91(Equation 7)7(-19b + 4c) = 7(-13) \implies -133b + 28c = -91 \quad (\text{Equation 7}) 4(−6b+7c)=4(3)  ⟹  −24b+28c=12(Equation 8)4(-6b + 7c) = 4(3) \implies -24b + 28c = 12 \quad (\text{Equation 8})

    Subtract Equation (8) from Equation (7):

    (−133b+28c)−(−24b+28c)=−91−12(-133b + 28c) - (-24b + 28c) = -91 - 12 −133b+24b=−103-133b + 24b = -103 −109b=−103-109b = -103 b=−103−109b = \frac{-103}{-109} b=103109b = \frac{103}{109}
  5. Substitute the value of bb into Equation (6) to find cc.

    −6(103109)+7c=3-6\left(\frac{103}{109}\right) + 7c = 3 −618109+7c=3-\frac{618}{109} + 7c = 3 7c=3+6181097c = 3 + \frac{618}{109} 7c=3×109109+6181097c = \frac{3 \times 109}{109} + \frac{618}{109} 7c=327+6181097c = \frac{327 + 618}{109} 7c=9451097c = \frac{945}{109} c=945109×7c = \frac{945}{109 \times 7} c=135109c = \frac{135}{109}
  6. Substitute the value of bb into Equation (4) to find aa.

    a=12−11ba = 12 - 11b a=12−11(103109)a = 12 - 11\left(\frac{103}{109}\right) a=12−1133109a = 12 - \frac{1133}{109} a=12×109109−1133109a = \frac{12 \times 109}{109} - \frac{1133}{109} a=1308−1133109a = \frac{1308 - 1133}{109} a=175109a = \frac{175}{109}

    The solution to the system of equations is:

    a=175109a = \boxed{\frac{175}{109}} b=103109b = \boxed{\frac{103}{109}} c=135109c = \boxed{\frac{135}{109}}
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