Question 1099379
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. . . then the angle x terminates in QIII, where sine is negative function, and 

sin(x) = {{{-sqrt(1-cos^2(x))}}} = {{{-sqrt(1-(-3/5)^2)}}} = {{{-sqrt(1-9/25)}}} = {{{-sqrt((25-9)/25)}}} -= {{{-sqrt(16/25)}}} = {{{-4/5}}}.
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