Find \(\mathrm{a}, \mathrm{b}\) and \(\mathrm{c}\) between 2 and 18 such that \(\mathrm{a}+\mathrm{b}+\mathrm{c}=25\), \(2, a, b\) are in A. P. and \(b, c, 18\) are in G. P. (A) \(5,8,12\) (B) \(4,8,13\) (C) \(3,9,13\) (D) \(5,9,11\)

Short Answer

Expert verified
The correct answer is (A) $a=5, b=8,$ and $c=12$.

Step by step solution

01

Formulate the Necessary Equations

Since 2, a, b are in A.P, we know that: a - 2 = b - a We can rewrite this as: 2a - b = 2 ---- (1) Similarly, since b, c, 18 are in G.P, we get: c/b = 18/c We can rewrite this as: c² = 18b ---- (2) Additionally, we are given the condition that a+b+c = 25, which we will use later.
02

Solve for Variable 'b'

To solve for variable 'b', multiply equation (1) by 18: 36a - 18b = 36 ---- (3) Now, substitute equation (2) into equation (3): 36a - c² = 36 Recall the given condition a+b+c = 25, which can be rewritten as: a+b = 25 - c Solve for c: c = 25 - a - b Substitute this back into the equation 36a - c² = 36: 36a - (25-a-b)² = 36 ---- (4)
03

Solve for Variables 'a' and 'c'

Now, we can substitute a = (b+2) from equation (1) into equation (4): 36(b+2) - (25-(b+2)-b)² = 36 Expand and simplify to get: 13b - b² = 8 ---- (5) We can try each option to see which one satisfies equation (5) for a, b, and c: (A) a=5, b=8, c=12 (B) a=4, b=8, c=13 (C) a=3, b=9, c=13 (D) a=5, b=9, c=11 Let's check each option: (A) 13(8) - (8)² = 8 (True) (B) 13(8) - (4)² = 8 (False) (C) 13(9) - (3)² = 8 (False) (D) 13(9) - (5)² = 8 (False) Only option (A) satisfies the equation, so the answer is: a = 5, b = 8, c = 12 (A)

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