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# If A, B, C Are in Continued Proportion, Prove that (A^2 + B^2 + C^2)/(A + B + C)^2 = (A - B + C)/(A + B + C) - ICSE Class 10 - Mathematics

#### Question

If a, b, c are in continued proportion, prove that (a^2 + b^2 + c^2)/(a + b + c)^2  = (a - b + c)/(a + b + c)

#### Solution

Given, a, b and c are in continued proportion.

=> a/b = b/c = k (say)

=> a = bk, b = ck

=> a = (ck)k = ck^2, b = dk

LHS = (a^2 + b^2 + c^2)/(a + b + c)^2

= ((ck^2)^2 + (ck)^2 + c^2)/(ck^2 + ck + c)^2

= (c^2k^2 + c^2k^2 + c^2)/(c^2(k^2 + k + 1)^2)

= (c^2(k^4 + k^2 + 1))/(c^2(k^2 + k + 1))

= (k^2 + k^2 + 1)/(k^2 + k + 1)^2

RHS  (a - b + c)/(a + b + c)

= (ck^2 - ck + c )/(ck^2 + ck + c)

= (k^2 = k^2 + 1)/(k^2 + k + 1)^2

LHS = RHS

Is there an error in this question or solution?

#### APPEARS IN

Selina Solution for Selina ICSE Concise Mathematics for Class 10 (2018-2019) (2017 to Current)
Chapter 7: Ratio and Proportion (Including Properties and Uses)
Ex.7C | Q: 10.2

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Solution If A, B, C Are in Continued Proportion, Prove that (A^2 + B^2 + C^2)/(A + B + C)^2 = (A - B + C)/(A + B + C) Concept: Proportions.
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