If sinA+tanA=p then sin2A?

3 answers

sinA + tanA = p
sinA + sinA/cosA = p
times cosA
sinAcosA + sinA = pcosA
sinAcosA = pcosA - sinA

but sin 2A = 2sinAcosA
= 2pcosA - 2sinA

??
if x = sinA
tanA = x/√(1-x^2)
cosA = √(1-x^2)

x + x/√(1-x^2) = p
x^2/(1-x^2) = (p-x)^2

quartics don't solve simply. If you go to wolframalpha . com and type

solve x^2/(1-x^2) = (p-x)^2

you will see a horrendous solution in terms of p.

Anyway, pick a solution and evaluate

2x√(1-x^2)
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