Cleachd foirmlean cur-ris/co-ionannachdan triantanachd gus abairtean triantanachd a shìmpleachadh/obrachadh a-mach. Fuasgail co-aontaran triantanachd le foirmle ceàrn dà-fhillte is fuincsean nan tonn.
Part ofMatamataigAbairtean agus fuincseanan
Feumaidh tu cuimhne a chumail air cuid de cho-ionannachdan triantanachd gus abairtean triantanachd a shìmpleachadh, no a dhearbhadh, nuair a dh'fheumas tu. 'S iad sin:
Seall gu bheil \(\sin \left( {x - \frac{{3\pi }}{2}} \right) = \cos x\)
\(\sin \left( {x - \frac{{3\pi }}{2}} \right)\)
\(= \sin x\cos \frac{{3\pi }}{2} - \cos x\sin \frac{{3\pi }}{2}\)
\(= \sin x \times 0 - \cos x \times - 1\)
\(= \cos x\)
Seall gu bheil \(\frac{{\sin (a + b)}}{{\cos a\cos b}} = \tan a + \tan b\) airson \(\cos a \ne 0\) agus \(\cos b \ne 0\)
\(\frac{{\sin (a + b)}}{{\cos a\cos b}} = \frac{{\sin a\cos b + \cos a\sin b}}{{\cos a\cos b}}\)
\(= \frac{{\sin a\cos b}}{{\cos a\cos b}} + \frac{{\cos a\sin b}}{{\cos a\cos b}}\)
\(= \frac{{\sin a}}{{\cos a}} + \frac{{\sin b}}{{\cos b}}\)
\(= \tan a + \tan b\)
