L\u1eddi gi\u1ea3i<\/strong><\/p>\n\n\n\nKhi \u03b2 = \u03b1 + k\u03c0 th\u00ec \u0111i\u1ec3m cu\u1ed1i c\u1ee7a g\u00f3c \u03b2 s\u1ebd tr\u00f9ng v\u1edbi \u0111i\u1ec3m T tr\u00ean tr\u1ee5c tan. Do \u0111\u00f3 <\/p>\n\n\n\n
tan(\u03b1 + k\u03c0) = tan\u03b1.<\/p>\n\n\n\n
Khi \u03b2 = \u03b1 + k\u03c0 th\u00ec \u0111i\u1ec3m cu\u1ed1i c\u1ee7a g\u00f3c \u03b2 s\u1ebd tr\u00f9ng v\u1edbi \u0111i\u1ec3m S tr\u00ean tr\u1ee5c cot. Do \u0111\u00f3 <\/p>\n\n\n\n
cot(\u03b1 + k\u03c0) = cot\u03b1.<\/p>\n\n\n\n
Tr\u1ea3 l\u1eddi c\u00e2u h\u1ecfi To\u00e1n 10 \u0110\u1ea1i s\u1ed1 B\u00e0i 2 trang 145<\/strong>: T\u1eeb \u0111\u1ecbnh ngh\u0129a c\u1ee7a sin\u03b1, cos\u03b1. H\u00e3y ch\u1ee9ng minh h\u1eb1ng \u0111\u1eb3ng th\u1ee9c \u0111\u1ea7u ti\u00ean, t\u1eeb \u0111\u00f3 suy ra c\u00e1c h\u1eb1ng \u0111\u1eb3ng th\u1ee9c c\u00f2n l\u1ea1i.<\/ins><\/p>\n\n\n\nL\u1eddi gi\u1ea3i<\/strong><\/p>\n\n\n\nsin\u03b1 = (OK) ;cos\u03b1 = (OH)<\/p>\n\n\n\n
Do tam gi\u00e1c OMK vu\u00f4ng t\u1ea1i K n\u00ean: <\/p>\n\n\n\n
sin2<\/sup> \u03b1 + cos2<\/sup> \u03b1 = OK2<\/sup> + OH2<\/sup> = OK2<\/sup> + MK2<\/sup> = OM2<\/sup> = 1.<\/p>\n\n\n\nV\u1eady sin2<\/sup> \u03b1 + cos2<\/sup> \u03b1 = 1.<\/p>\n\n\n\n