If roots of  are equal in magnitude and opposite in sign, then which of the following is true ?

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RPSC 2nd Grade Mathematics (Held on 18th Feb 2019) Official Paper
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  1. p + q = 2r
  2. p + q = −2r
  3. p + q = 0
  4. p = r − q

Answer (Detailed Solution Below)

Option 1 : p + q = 2r
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RPSC Senior Grade II (Paper I): Full Test 1
100 Qs. 200 Marks 120 Mins

Detailed Solution

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Given:

The roots of  are equal in magnitude and opposite in sign

Concept:

For any quadratic equation let us say

ax2 + bx + c = 0

Sum of the roots = -b/a

Product of the root = c/a

Solution:

⇒ 

⇒ 

⇒ 

Comparing above with ax2 + bx + c = 0 we will get, 

a = 1, b = (p + q -2r), c = [pq + (p + q) r]

According to the question, the roots of the given equation are equal in magnitude and opposite in sign

Let say  be the roots, then

Sum of the roots = [] = 0 = -b/a

⇒ -b/a = -(p + q - 2r) = 0

p + q = 2r

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