- 三角证明题求证(sina)^2
- 求证 (sina)^2-(sinb)^2=tg(a+b)(sinaca-sinbcosb)
- 求证 (sina)^2-(sinb)^2=tg(a+b)(sinacosa-sinbcosb)
证明:右=sin(a+b)(sinacosa-sinbcosb) /cos(a+b)
=(sina*cosb+cosa*sinb)(sinacosa-sinbcosb)/(cosa*cosb -sina*sinb)
=(sina)^2-(sinb)*(cosa*cosb-sina*sinb) /(cosa*cosb -sina*sinb)
=(sina)^2 - (sinb)^2
=左