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Answer:
-
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 × - ×
= = -