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Question
If m - n = 0.9 and mn = 0.36, find:
m + n
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Solution
Given m - n = 0.9 and mn = 0.36
(m - n)2 = m2 - 2mn + n2
⇒ (0.9)2 = m2 - 2mn + n2
⇒ 0.81 = m2 + n2 - 2(0.36)
⇒ 0.81 = m2 + n2 - 0.72
⇒ m2 + n2 = 1.53
So, (m + n)2 = m2 + 2mn + n2
⇒ (m + n)2 = m2 + n2 + 2mn
⇒ (m + n)2 = 1.53 + 2(0.36)
⇒ (m + n)2 = 2.25
⇒ m + n = ±1.5.
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