If p2 + q2 = 1 and m2 + n2 = 1, then

  1. |pm + qn| ≤ 0
  2. |pm + qn| ≤ 1
  3. |pq + mn| > 1
  4. |pq + mn| < 2

Answer (Detailed Solution Below)

Option 2 : |pm + qn| ≤ 1
Free
General Knowledge for All Defence Exams (शूरवीर): Special Live Test
20 Qs. 20 Marks 16 Mins

Detailed Solution

Download Solution PDF

Given:

p2 + q2 = 1

m2 + n2 = 1

Formula used:

sin2θ + cos2θ = 1

cos(A + B) = cos A cos B - sin A sin B

-1 ≤ cos θ ≤ 1

Calculation:

Let

p = cos θ, q = sin θ 

m = cos ϕ, n = sin ϕ 

Therefore,

⇒ pm + qn = cos θ cos ϕ + sin θ sin ϕ 

⇒ pm + qn = cos(θ - ϕ)

∵ -1 ≤ cos θ ≤ 1

⇒ -1 ≤ pm + qn ≤ 1

⇒ |pm + qn| ≤ 1

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