Если sinA=-40/41, tgB=9/40, A∈Ⅳч, то чему равен tg (a+b)

Sina=-40/41

tgb=9/40; a€|V

tg (a+b) = (tga+tgb) / (1-tga*tgb) = ?

cos²a=1-sin²a=1-1600/1681=81/1681

cosa=9/41; a€|V

tga=sina/cosa=-40/41:9/41=-40/9

tg (a+b) = (-40/9+9/40) (1+9/40*40/9)

= (-1600+81) / (2*360) =

-1519/720

sinα = - 40/41; tgβ = 9/40

cosα = √ (1 - cos²α) = √ (1 - 40²/41²) = √ ((41² - 40²) / 41²) = √ ((81) / 41²) = 9/41;

tgα = sinα/cosα = - 40/9

tg (α+β) = (tgα + tgβ) / (1 - tgα · tgβ) = (-40/9 + 9/40) / (1 + 40/9 · 9/40) = - 1519 / (2 · 360) = - 1519/720