Bai_21_DABTTL_He_PT_mu_logarit_Phan_02

# Bai_21_DABTTL_He_PT_mu_logarit_Phan_02 - Kha hc Ton 12 Thy...

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Khóa h c Toán 12 Th y Lê Bá Tr ần Phương H phương trình mũ - logarit Hocmai.vn Ngôi trườ ng chung c a h c trò Vi t T ổng đài tư vấ n: 1900 58-58-12 - Trang | 1 - II. Đặt ẩn phụ 1. 3 3 log y log x 3 3 x 2y 27 log y log x 1 Giải: ĐK: x, y > 0 Đặt 3 3 log x u log y v u v x 3 y 3 Khi đó ta có hệ: u v u v 3 2.3 27 v u 1 uv 3.3 27 v u 1 uv 3 9 v u 1 uv 2 (1) v u 1 (2) Từ (2) v = 1 + u, thế vào (2) ta có: u(1 + u) = 2 2 u u 2 0 u 1 v 2 u 2 v 1        + Với u 1 x 3 v 2 y 9 + Với 2 1 1 x 3 u 2 9 v 1 1 y 3 3     Đáp số: (3, 9); 1 1 , 9 3 .

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