Trigonometric Ratios of Allied Angles: Relation between θ and -θ
if cos θ = 12...
Question
ifcosθ=1213andθ∈(0,π2],then144(tan(−θ)×sec(−θ)]
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Solution
Given,θ∈(0,π2]
This means θ lies in first quadrant. cosθ=1213⇒sinθ=√1−122132⇒sinθ=513⇒tanθ=sinθcosθ=512andsecθ=1cosθ=1312
Also we know, tan(−θ)=−tanθandsec(−θ)=secθ
Thus, tan(−θ)×sec(−θ)⇒−tanθ×secθ
Substituting values we get, −tanθ×secθ=−512×1312=−65144⇒144tanθ×secθ=−65144×144⇒144tanθ×secθ=−65