Jika 2sinx + 2 cosx = a, maka harga dari sin 2x

[tex]sin 2x = 2sinxcosx \\ 2sinx+2cosx = a \\ sinx + cosx = \frac{a}{2} \\ (sinx+cosx)^{2} = \frac{a^2}{4} sin^{2}x+2sinxcosx+cos^2x=\frac{a^2}{4} \\ sin^{2}x+cos^2x+2sinxcosx=\frac{a^2}{4} \\ 1 + 2sinxcosx=\frac{a^2}{4} \\ 2sinxcosx=\frac{a^2}{4} - 1 \\ sin2x=\frac{a^2}{4} - 1 [/tex]