Minimum value of sintheta+cosec theta whole square +cos theta +sec theta whole square
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it is given that (sinθ + cosecθ)² + (cosθ + secθ)²
we have to find the minimum value of above expression.
(sinθ + cosecθ)² + (cosθ + secθ)²
= sin²θ + cosec²θ + 2sinθ. cosecθ + cos²θ + sec²θ + 2cosθ. secθ
we know, cosecθ. sinθ = 1 and cosθ. secθ = 1
= (sin²θ + cosec²θ) + 2 + (cos²θ + sec²θ) + 2
= (sin²θ + cosec²θ) + (cos²θ + sec²θ) + 4
we know, sin²θ , cosec²θ are positive
so AM ≥ GM
(sin²θ + cosec²θ)/2 ≥ √(sinθ. cosecθ)
⇒sin²θ + cosec²θ ≥ 2
so minimum value of sin²θ + cosec²θ = 2
similarly you can get minimum value of cos²θ + sec²θ = 2
now minimum value of (sin²θ + cosec²θ) + (cos²θ + sec²θ) + 4
= 2 + 2 + 4
= 8
hence minimum value of (sinθ + cosecθ)² + (cosθ + secθ)² = 8
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