Question 923632
sin x = 1/7,  cos x > 0, cos x = 4√3 /7 {{{sqrt(7^2 - 1^2) = sqrt(48)}}}
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 sin y = &#8722;2/5, and cos y < 0, cosy = &#8730;21 / 5  {{{sqrt(5^2 - 2^2) = sqrt(21)}}}
........Plug and Play
sin(x + y) = sin x cos y + sin y cos x
sin(x + y) = (1/7)(&#8730;21 /5)  + (-2/5)(4&#8730;3 /7)