If cosa = 3/5 and a ∈ (630,720), find sin2a

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Step-by-step explanation:

Given 630 < A > 720 then A is in the fourth quadrant where

cosA > 0 and sinA < 0

Given

cosA = =

Then the triangle is a 3- 4 - 5 with opposite side 4, thus

sinA = - = -

Using the trigonometric identity

sin2A = 2sinAcosA

         = 2 × - ×

         = = -

answer;

the correct answer

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