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Let numbers a(1),a(2)…a(16) are in AP an...

Let numbers `a_(1),a_(2)…a_(16)` are in AP and `a_(1)+a_(4)+a_(7)+a_(10)+a_(13)+a_(16)=114` then `a_(1)+a_(5)+a_(12)+a_(16)` is equal to

A

36

B

96

C

76

D

38

Text Solution

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The correct Answer is:
To solve the problem, we start with the information given about the arithmetic progression (AP) and the specific sums of its terms. ### Step 1: Understand the terms in the AP Let the first term of the AP be \( a_1 \) and the common difference be \( d \). The terms can be expressed as: - \( a_1 = a_1 \) - \( a_4 = a_1 + 3d \) - \( a_7 = a_1 + 6d \) - \( a_{10} = a_1 + 9d \) - \( a_{13} = a_1 + 12d \) - \( a_{16} = a_1 + 15d \) ### Step 2: Write the equation for the given sum We are given that: \[ a_1 + a_4 + a_7 + a_{10} + a_{13} + a_{16} = 114 \] Substituting the expressions for the terms, we get: \[ a_1 + (a_1 + 3d) + (a_1 + 6d) + (a_1 + 9d) + (a_1 + 12d) + (a_1 + 15d) = 114 \] ### Step 3: Simplify the equation Combining like terms, we have: \[ 6a_1 + (3d + 6d + 9d + 12d + 15d) = 114 \] The sum of the coefficients of \( d \) is: \[ 3 + 6 + 9 + 12 + 15 = 45 \] Thus, we can rewrite the equation as: \[ 6a_1 + 45d = 114 \] ### Step 4: Solve for \( a_1 + a_4 \) and \( a_{13} + a_{16} \) We can express \( a_1 + a_{16} \) and \( a_4 + a_{13} \): \[ a_1 + a_{16} = a_1 + (a_1 + 15d) = 2a_1 + 15d \] \[ a_4 + a_{13} = (a_1 + 3d) + (a_1 + 12d) = 2a_1 + 15d \] This shows that: \[ a_1 + a_{16} = a_4 + a_{13} = a_7 + a_{10} \] ### Step 5: Relate the sums Since \( a_1 + a_4 + a_7 + a_{10} + a_{13} + a_{16} = 114 \) can be grouped as: \[ (a_1 + a_{16}) + (a_4 + a_{13}) + (a_7 + a_{10}) = 114 \] This can be rewritten as: \[ 3(2a_1 + 15d) = 114 \] Dividing both sides by 3 gives: \[ 2a_1 + 15d = 38 \] ### Step 6: Find \( a_1 + a_5 + a_{12} + a_{16} \) Now we need to find: \[ a_1 + a_5 + a_{12} + a_{16} \] Expressing \( a_5 \) and \( a_{12} \): - \( a_5 = a_1 + 4d \) - \( a_{12} = a_1 + 11d \) Thus, we have: \[ a_1 + a_5 + a_{12} + a_{16} = a_1 + (a_1 + 4d) + (a_1 + 11d) + (a_1 + 15d) \] Combining these terms gives: \[ 4a_1 + (4d + 11d + 15d) = 4a_1 + 30d \] ### Step 7: Substitute \( 2a_1 + 15d \) We know from the earlier step that \( 2a_1 + 15d = 38 \). Therefore: \[ 4a_1 + 30d = 2(2a_1 + 15d) = 2 \times 38 = 76 \] ### Final Answer Thus, the value of \( a_1 + a_5 + a_{12} + a_{16} \) is: \[ \boxed{76} \]
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